I just installed my lift pump yesterday, and it got me to thinking about the optimum way to regulate pressure. I need to give some background first.


Almost 10 years ago my wife's car was a '74 Jag XJ12 with a Chevy 350 I had built. I installed a Moroso 110 gph, self-regulating electric fuel pump and ran it unregulated to the Q-Jet carb. Within a year of the pump install,the car stranded my wife one day becasue the fuel pump failed--the brass plunger that regulated the pressure had worn out it's aluminum seat.


Super Shops warrantied the pump and to avoid a similar situation, I fixed the pump so the pressure regulating plunger was locked down, making this 7 PSI pump a 9.5 PSI pump. Well, fuel pressure to the Q-Jet really should be kept around 6 psi max, so I installed a pressure gauge and one of those Holley "blue" regulators, setting it to 5.25 PSI.


Well, the fuel pressure never remained consistent at idle. Sometimes it would be 4 psi, sometimes over 6. My fix for that is what will apply well to our lift pumps. I installed a "T" in the fuel line between the fuel pump and the carburettor. I then installed the regulator on this "T", and ran a line from the downside of the regulator to the tank return line. I kept the pressure gauge between the "T" and the carb.


What this made was a variable demand bypass system. The pressure at idle stayed rock steady at 5.25 PSI. As fuel demand inceased, fuel volume increase as well up to the limit of the pump, but without a drop in pressure.


The needle valve set-ups may are running on the DMax do lower the pressure, but the do so at the expense of limiting fuel volume. The needle is closed and pressue is reduced, but because the needle is sitting in the outflow portion of the fuel line to the injector pump, it is a constant restriction. When the engine wants more fuel, it can only get as much as is able to get by the needle valve. Perhaps this is why guys running this set up sometimes see a vaccuum.


I think a better way would be to "T" into the line somewhere between the lift pump and the injector pump, and install a regulator on that "T"ed in line. The line would not necessarily have to go back to the tank, it could be looped around and "T"ed into the line on the suction side of the lift pump. I don't know if there would be a problem with backflow this way, perhaps a check valve would need to be installed. Reagrdless, tapping into the fuel return line to the tank would not cause a backflow problem. Maybe another port could be tapped into the Mega or CAT or Raycor filter housing for this line?


This set-up would bypass fuel the most at idle, and would bypass less and less fuel and the engine fuel demand increased. It would keep the PSI at the injector pump constant until we ran out of lift pump.


If it would help, I'll upload a drawing...............


Blaine

As soon as it warms up enough I'm going to install my lift pump with a check valve located between the OEM and my MEGA. The check valve has a 5psi cracking pressure. I will return the line to the tank. I may even tee the return from the engine into this line and get it away from the pickup in the tank. Of course I may even go with one of the air separators should they prove to be an efficient investment.

Good post Blaine! I was wondering when someone was going to figure this one out. I don't run a lift pump so I have kept my .02 out of the discussion. Later! Frank

Dave,


The return line returns to a cup where the main fuel suction draws from. It basicly keeps the cup full to prevent the main suction from pulling in air when the tank is low and sloshing. I had also thought about moving this line untill I saw how the sender was designed but then quickly changed my mind. I was also going to use an adjustable pressure cracking check which I still have on the shelf. I also scratched this plan when I saw my pump delivered only 6 PSI @ the pump.

Bypass regulators have been used for years in the raceing industry, just as Blaine has described it. As a matter of fact they worked so well that Nascar banned them. The trick is to make sure you have enough pump to allow them to work properly and that's where the problem lies. Most of the higher volume pumps are designed for short period use. We have been researching for a good source for a 12 vdc electric pump that is designed to pump 220 GPH and have a motor life of a min. of 3000 hours. The closest we have found so far is the FASS and PREPORATOR units. Both flow 160 GPH and are rated at 3000 hour motor life. This is enough for most of the regular trucks but not enough for the High Hp guys.


The Duramax has a return fuel system that will bleed fuel off the supply line to cool the injectors but that also uses up needed volume so the supply pump must take that into account. They are big units and the only place we have found to mount them is in the rear driverside fenderwell. You must fab your own brackets to support them as they are about 25 lbs when full of fuel. Something you donot want falling off when your traveling a rough road. They both use a return type regulator built in to each unit and it must be connected to the tank. One way is to make a sleeve that goes into the filler tube with a hose barb for the return fuel. This works OK but it does screw with filling the tank if you leave the truck running. There is an extra fitting on the fuel sender that is blocked off but can be drilled to open it up and return the fuel at that point. We are getting ready to test that option in the near future.

Diesel Tech,


What about a pair of lift pumps or other smaller pumps run in parallel?


How much are the 160 GPH pumps?


Blaine

We though about two pumps but the problem is what to do if one or two quit and your on the road. Both the Preporator and Fass units have built in bypass if the pump fails, a good feature and hard to implement with twin pumps in parallel. I think if we continue to look something will show up, if not I will just make one for myself. I'm lucky enough to have the tools and machinery necessary to make one! I know it's not the answer everyone is looking for but so far it's the best I've come up with.

Hello,


This is the piece Diesel tech decribed. 3.5"L X 2.0" O.D. 2.5"L X .5" O.D. It goes in the filler neck.


http://www.dieselplace.com/forum/uploads/6ZC_P3080033.jpgEdited by: Bronco

What would be really cool is if you could run one pump to the engine and one pump to recirc the fuel out of the tank through a cat filter and back into the tank. The second pumps job would be solely to clean the fuel. You might get the fuel recirculated 300-3000 times before it gets to the injectors. ISO would be 1-1-1.

And maybe we could make drinking water out of diesel too ...


Why not bring back the simple 520 HP set-up of yester-year ?? http://www.dieselplace.com/forum/smileys/Wink.gif





Mac

…The needle valve set-ups may are running on the DMax do lower the pressure, but the do so at the expense of limiting fuel volume. The needle is closed and pressure is reduced, but because the needle is sitting in the outflow portion of the fuel line to the injector pump, it is a constant restriction. When the engine wants more fuel, it can only get as much as is able to get by the needle valve. Perhaps this is why guys running this set up sometimes see a vacuum…

Blaine,

The needle valve in the "a bear" bypass regulator that many of us are using is in the in the bypass loop - it's not between the Lift pump and the OEM pump therefore it does not restrict flow. We have a tee at the output of the lift pump. The "thru" path of the tee goes directly to the main fuel line feeding the OEM pump. The needle valve controls the amount of fuel that bypassed around the pump to regulate pressure at the output. The output of the needle valve is fed back to the lift pump input with a tee or in my case though the second input port of the prefilter. See liftpump/prefilter (http://community.webshots.com/photo/77018086/77108574VFZuzV) for more detail.
This is not to say that this setup can't be improved, but this approach completely eliminated the vapor accumulation I was seeing in my mega filter. It also makes the engine start quicker and run smoother/quieter.

http://www.dieselplace.com/forum/smileys/Geek.gif Edited by: jbplock

I wish I would go ahead and win the lottery. I would put a pressure transducer on and send the data to a chart recorder for a couple of weeks. Then we could really know what's going on. I'm just to cheap to drop that kind of cash just to know. For that kind of money, you can get a Juice or half a Tranny upgrade or a quarter of a new tranny or ........ Never stops, huh?

afp1,


The NV in the bypass loop provides a ECONOMICAL means to safely control pressure to the engine LP gear pump. Although it is not a precise regulator it is somewhat self adjusting. As fuel demand goes up the pump outlet pressure will drop somewhat and allow less pressure diffriential pressure across the NV which in turn would recirculate less and allow more fuel to go to the engine and vis-versa. You actually see less pressure sweep than running a lift pump alone. I would be the first to admit that the fuel pressure can be better controlled with a regulator but it would be at a greater cost and I have yet to find a LOW PRESSURE regulator compatable w/ diesel fuel. Minor fluctuations in pressure upstream of the LP gear pump has no effect on the pressure between the gear pump and the HPCR pump and so on due simply to the fact that the gear pump is pos. disp. and fluid does not compress. There are even larger pressure fluctuations on systems that run no lift pump due to changes in load, braking and inertia. The pressures under vac also sweep readily. (Doesn't hurt a thing) If someone was to run the AC Delco EP309 lift pump which has the built in pressure regulator set to about 6 Psi there may be no need for a bypass at all. I would have no problem running this pump w/o the bypass. Many here are already running other pumps w/o bypasses and discharging at pressures up to 16 PSI and so far things seem to be fine but I tend to approach things more cautiously.

I wish I would go ahead and win the lottery. I would put a pressure transducer on and send the data to a chart recorder for a couple of weeks. Then we could really know what's going on. I'm just to cheap to drop that kind of cash just to know. For that kind of money, you can get a Juice or half a Tranny upgrade or a quarter of a new tranny or ........ Never stops, huh?


I did it the cheap way out........... Remove the Factory fuel test port, remove the rubber hose conection on bottom and adapt to a standard 1/8" pipe thread, install pressure/vacum gauge and hose to fitting. This allows you to have a gauge in the vehicle and see what's going on. I can tell you that it doesn't look pretty. When you add power adders it just gets worse. The end result is the High pressure side of the fuel pump is overworked to try and stay up with the demand and this we have data logged. By solveing the supply problem to the high pressure pump we have made smoother running engines and for you Hp junkies 500 + RwHp on good old #2

I did it the cheap way out........... Remove the Factory fuel test port, remove the rubber hose conection on bottom and adapt to a standard 1/8" pipe thread, install pressure/vacum gauge and hose to fitting. This allows you to have a gauge in the vehicle and see what's going on. I can tell you that it doesn't look pretty. When you add power adders it just gets worse. The end result is the High pressure side of the fuel pump is overworked to try and stay up with the demand and this we have data logged. By solveing the supply problem to the high pressure pump we have made smoother running engines and for you Hp junkies 500 + RwHp on good old #2


Okay, I'll bite. Pictures of your setup? Data you took? Did you have any concerns with taking a fuel line into the cab? I have a lift pump already, so I know I'm in better shape than most, but ........Edited by: chuntag95

No pictures, sorry. I didnot intend on leaveing it in the truck forever, it was just for testing so fuel in the cab didn't bother me. Heck in the old days we used to run fuel pressure gauges in the car all the time. If you want to be safer you can get an electric sender and keep the fuel underhood. If you look at the pasengerside front of the motor you will see the factory fuel test port. It's the one with the black plastic cover on it. It is held in place by two studs with 12 mm nuts. Remove the nuts and lift mount block up. On the bottom of the block you will find a rubber fuel line connection held on with a hose clamp. Remove the hose from the block and install a hose fitting to 1/8" pipe thread fitting into the hose and clamp from there you will need to adapt to whatever fittings you will need for your gauge setup. I used a standard Vacumn Pressure fuel gauge and 1/8" plastic hose setup they sell for fuel or oil pressure gauge kit. Route the hose into the cab and mount gauge where you want it.


On a stock truck you will see vacumn on the gauge. As you run the engine harder the guage will show what's happening. I believe GM says not to exceed 8" vacumn(not sure on the exact number). If you run a lift pump you donot need a Vacumn/Pressure gauge only a pressure gauge. If you supply enough volume to the high pressure pump the pressure should never change on your gauge. If it drops any amount then your not supplying enough volume. Bosch and Cummins state to run 13 - 15 psi on the common rail pressure feed line. I am alittle worried about the EDU on the GM application leaking so I keep the pressure set to 5 psi. That's 5 psi at idle or WOT!


The data was posted some time ago here on the site by Nick (Diesel Power)showing what happens to the high pressure when the supply drops. You would need to do a search to find it again. I will ask Nick to post a link for those who wish to look at the data again.

No pictures, sorry. I didnot intend on leaveing it in the truck forever, it was just for testing so fuel in the cab didn't bother me. Heck in the old days we used to run fuel pressure gauges in the car all the time. If you want to be safer you can get an electric sender and keep the fuel underhood. If you look at the pasengerside front of the motor you will see the factory fuel test port. It's the one with the black plastic cover on it. It is held in place by two studs with 12 mm nuts. Remove the nuts and lift mount block up. On the bottom of the block you will find a rubber fuel line connection held on with a hose clamp. Remove the hose from the block and install a hose fitting to 1/8" pipe thread fitting into the hose and clamp from there you will need to adapt to whatever fittings you will need for your gauge setup. I used a standard Vacumn Pressure fuel gauge and 1/8" plastic hose setup they sell for fuel or oil pressure gauge kit. Route the hose into the cab and mount gauge where you want it.


On a stock truck you will see vacumn on the gauge. As you run the engine harder the guage will show what's happening. I believe GM says not to exceed 8" vacumn(not sure on the exact number). If you run a lift pump you donot need a Vacumn/Pressure gauge only a pressure gauge. If you supply enough volume to the high pressure pump the pressure should never change on your gauge. If it drops any amount then your not supplying enough volume. Bosch and Cummins state to run 13 - 15 psi on the common rail pressure feed line. I am alittle worried about the EDU on the GM application leaking so I keep the pressure set to 5 psi. That's 5 psi at idle or WOT!


The data was posted some time ago here on the site by Nick (Diesel Power)showing what happens to the high pressure when the supply drops. You would need to do a search to find it again. I will ask Nick to post a link for those who wish to look at the data again.





I would have to disagree on this one. If the pressure @ WOT drops somewhat you are not starving the engine of fuel as with a carburated/injected gas engine. The gear LP pump that feeds the HPCR pump is positive displacement with a fixed volume of more than the engine needs @ max load plus allowing needed return volume based on the given RPM. If even zero registers on the gauge you are still providing more volume than what was given during the stock set up (under vac) The volume provides the pressure so if the pressure is there (above stock vac) then more volume is too......Edited by: a bear

Any pressure above the stock system's pressure (negative) will insure that the mega is completely full and the system doesn't have too much suction head. I think I said that right. Later! Frank

Needle Valve works for me and is a simple and cheap install. Adjust pressure where you want it and forget it. Check pressure every couple of weeks and if it is falling it is a good indication that you filter is plugging. You guys are making a simple job into a high tech head ache. If you are running the cat filter there is a port on the outlet side where the needle valve can be installed and returned to the suction side of the pump.


Geno

What would be really cool is if you could run one pump to the engine and one pump to recirc the fuel out of the tank through a cat filter and back into the tank. The second pumps job would be solely to clean the fuel. You might get the fuel recirculated 300-3000 times before it gets to the injectors. ISO would be 1-1-1.


Hey PC,


You are more correct then you know! The FASS at 144GPH and The Prep at 158GP are both already doing this. The feed line to the engine is completely unrestricted. The return line to the tank is the part with the regulator. Being that these units always flow full volume, regardless of RPM, at idle a signigant amount of fuel is being passed through the filters and directly back to the tank. Even at WOT there is fuel that will go straight from the filter to the tank. In marine applications the PREP is used as a fuel polisher during periods of inactivity. Basically if you filled your tank completely and used a FASS or PREP you would most definatly refilter your fuel sevaral times. Just take the average engine demand and subtract from 150GPH. So lets say the Dmax uses an average of 7GPH. In one hour 143 gallons would have been filtered and returned to the tank.


This is why 2 things are critical. First any fuel sample has to be conducted with some sort of standard. Multipass fuel will always be cleaner then singlepass fuel. Secondly if the Fass or Prep does not remove air at all RPMs. you are actually hurting your motor by constantly ariating and heating your fuel for no reason. If one of these units were defective you could be adding air to your fuel.Edited by: Bronco

I don't see why the Holley blue or similiar inexpensive regulator wouldn't work for the bypass. One of the Holleys can be set between 1 and 4 PSI, which should work great. I don't think the PSI is that big of a deal when we are talking under 15 psi static.


I do like the idea of returning to the filler cap or the empty fitting on the fuel sender, although PCs idea of running a bypass fuel filter is good as well.


Blaine

AFP 1,


Sorry for getting off topic. I have also wondered if a guy could not regulate the return effectively. Build a filler neck gizmo like the one pictured above or tap into the top of the fuel tank. The good thing about the top of the fuel tank is leaks are no problem. Unless your truck is upside down! I have searched for regulators before. Holey and Summit both sell very cheap low pressure regualator. Less than 30 bucks. I have even wondered if a cheap dial purolator type would work?

I would be very carefull in the selection of a LP regulator for a diesel application. With the soft goods of these regulators being designed for gasoline the diesel may swell and eat them away over time. I would make sure the soft goods are Buna-n at the least or even Viton better yet. I keep calling it a regulator but I guess if it is installed in the bypass loop it would become a PSV. Edited by: a bear

I was considering a Holley "blue" pump before I got the AC Delco and if memory serves I think the box or the salesman(maybe the salesman was a box)http://www.dieselplace.com/forum/smileys/Clown.gif said that it is diesel fuel compatible.


I think the regulator ought to be too.


Just my .02.


Blake

Aliphatic Petroleum Distillates will slowly eat away many of the rubber compounds that are compatable w/ gasoline, however some will last for a while. I would make sure the rubber componets are a quality elastomer specifically for diesel fuel then there would be no long term problems. Edited by: a bear

Compatability with diesel and our additives is the biggest concern--I wonder if those compatible with alcohol would work?

a bear


If the supply pump is dropping pressure as the engine runs up you are short on volume, if you had enough volume the pressure would hold constant, basic supply and demand design. I didn't say it was short for the engine demand and as you stated as long as it's positive there is enough(for stock applications). The only problem with that is the computer is trying to hold a certain prerssure on the outlet side. As the inlet pressure drops it has to correct for it. Once the system begins to servo back and forth the output is not constant. The better the inlet pressure is at being stable the better the outlet pressure will be and the smoother the engine will run. If you set your system at 5 psi and it drops dureing acceleration to 3 you are much better off to set the regulator to 3 so it will stay the same at all time, The control loop become much more stable at this point in time which allows the injection time to be much more accurate. All one needs to do is look at the data on the predicted output of the high pressure pump to the real pressure and you can see the loop trying to control. Adding a supply pump with a controlled inlet pressure makes a huge improvement and adds the necessary capacity for the Hp junkies to have fun.

Diesel Tech,


There is no pump made (practicle) that will compensate for pressure fluctuations brought on by rapid inertia and breaking. Thats why in the race industry fuel tanks are mounted up front with the engine. With a positive displacement LP pump being that which feeds the HPCR pump changes in pressure at the lift pump within the ranges we are talking about will not affect this LP pumps volume/output pressure. Simply because the LP pump is a pos displacement pump that will move a fixed volume with corresponding pressure per revolution. All this is based on the simple fact that liquid will not compress. There is one member here that recorded a peak vac of 25" HG while making a hard take off with no change in performance due to the fact that the system continued to deliver the needed supply. I do believe in the benefits of running a lift pump. I am simply stating that installing a monster pump to maintain full pressure with no drop is simply not needed for measurable gain.

Diesel Tech


Ole faithfull =>http://www.dieselplace.com/forum/uploads/ZA3_Red.jpg


White GMC Sierra 2001 ring a bell ?? Salty ??


Mac http://www.dieselplace.com/forum/smileys/Shocked.gif





Edited by: Mackin

So which regulators are diesel compatible? What about the ones rated for alcohol?

Good post a bear. Basic hydraulics. Later! Frank

a bear


I guess we will have to agree to disagree. If you take the time to do some simply testing you will find your wrong. I've done the testing and provided the data to show others. Nick (Diesel Power) has posted the results of both before and after fuel pressure data logs of the high pressure pump output. The stock system was tested and was within GM specification on inlet suction. Do you call a 9000 psi pressure drop acceptable on the outlet? The addition of the lift pump dropped the high pressure variation to within 500 psi of commanded until the inlet pressure to the High pressure pump drops off. Once the inlet pressure falls off so does the outlet of the High pressure pump!We are testing the inlet pressure at the factory test port in all cases and data logging the high pressure pump with a Tech II tool.The data speaks for it self.

a bear


I guess we will have to agree to disagree. If you take the time to do some simply testing you will find your wrong. I've done the testing and provided the data to show others. Nick (Diesel Power) has posted the results of both before and after fuel pressure data logs of the high pressure pump output. The stock system was tested and was within GM specification on inlet suction. Do you call a 9000 psi pressure drop acceptable on the outlet? The addition of the lift pump dropped the high pressure variation to within 500 psi of commanded until the inlet pressure to the High pressure pump drops off. Once the inlet pressure falls off so does the outlet of the High pressure pump!We are testing the inlet pressure at the factory test port in all cases and data logging the high pressure pump with a Tech II tool.


The data speaks for it self.


Read further and I think you will see I am not wrong. Yes a 9000 Psi drop is accepted on a variable pressure system. Again the flow from the POSITIVE displacement LP pump is variable based on engine RPM. Pressures also vary in the HPCR as dictated by the ECM to provide Precise VARIABLE injection pressures based on Load/RPM. It does not run @ 23000 PSI constantly.



<BLOCKQUOTE>How Direct Injection Works</BLOCKQUOTE>
<UL>
<LI ="disc">The fuel is drawn from the tank by the low-pressure pump through the Electronic Driver Unit (EDU). The fuel cools the electronics, which actuate solenoid valves in each injector, sometimes over 25 times per second.


<LI ="disc">The EDU works with the Engine Control Module (ECM) to provide a strong, precise signal for each cylinder's combustion event. The ECM also controls pressure in the fuel rail to ensure that it will be correct for precise fuel metering.


<LI ="disc">From the EDU, the fuel passes through an engine-mounted fuel filter. This filter has a water sensor, a water separator and a fuel heater. If necessary, the heater warms the fuel to 57 degrees Fahrenheit to prevent any waxing of the fuel.


<LI ="disc">The fuel then goes to the Bosch high-pressure pump. If the ECM and EDU are the brains of the system, the Bosch high-pressure pump is the heart. It sends the fuel to the fuel rails, variably controlled at pressures up to 23,000 psi, where it is distributed to the injectors at each cylinder.


<LI ="disc">The injector, with a constant injection pressure fed to it, can now open, stay open and close as directed by the ECM and EDU, depending on various sensor inputs, to achieve effective combustion for the conditions present.


<LI ="disc">The injector is optimally located in the cylinder head, and configured with a custom-designed spray pattern matching the combustion chamber, to gain the most efficient combustion. This enables improved fuel efficiency, lower emissions, and less heat loss and rejection. </LI>[/list]


On Edit : As you have suggested I have done a lot of testing. It's what I do for a living. If you would like I can provide pics of different systems I have been instrumental in designing and facility acceptance testing. Frankly I will not take this any further. Pump away ! GM must have missed this one.Edited by: a bear

Hello Abear,


You are obviously familar with the fuel system on our trucks. I have a few questions for you , if you do not mind. This entire air thing is of great interest to me. However it is hard to find good information. One thing I have learned, that many have missed is the folowing. The air is already in the fuel. It is pressure differences in the system that cause the air to come out of the fuel. Many get hung up on terminology such as offgas,vapor,vacum,pressure,cavitation and air leaks.


The simple fact is, if you create a pressure difference, then the air has an oppurtunity to separate. Just look at certain aftermarket fuel filters. They prove that air can and is being separated from the fuel. With that in mind, here are my questions to you.


1. After the factory fuel filter, where exactly does fuel go?


2. Can you decribe the factory pump? ( From what I can tell it is no ordinary pump. It is more of a two stage with varible inlet)


3. Can you decribe the regulator and its postioning to the factory lift pump?


I only ask these questions because I have never had these componets in my hands. I have only looked at pictures and diagrams.


I am curios if GM's factory fuel system already includes simple design features that facillitate air removal. I am also curious if an extra lift pump would actually solve cavitation at the factory pump inlet like it would on a older regular style factory gear pump? It almost seems like our factory pump would create it's own unique issues only applicable to the GM system and cavitation at pump inlet might not be a problem?


Finally one more question, your very last sentence in the above post said that GM must have missed this one. What did you mean? Without body language I am having trouble putting it into context?


Thanks


Jeff

a bear


"The fuel is drawn from the tank by the low-pressure pump through the Electronic Driver Unit (EDU). "


You must be taking this information from a Bosch description, as GM doesnot have a low-pressure pump in the system! http://www.dieselplace.com/forum/smileys/Ermm.gif So what we are doing is adding the low pressure pump that Bosch had called for in the first place! GM must have figure it works OK without it so let's save a few bucks! Cummins uses the same system but runs the low pressure pump. If you follow the Bosch manual it specs. the low pressure supply to be 13 - 15 psi, not 0 - 15 psi.


"The injector, with a constant injection pressure fed to it, can now open, stay open and close as directed by the ECM and EDU, depending on various sensor inputs, to achieve effective combustion for the conditions present. "





This is the key to the whole system, constant pressure! The 9000 psi loss I have described to you is not acceptable. The system commands a fixed pressure to be at the injector and the regulator adjust to that pressure. What I am describing (possible not good enough to you) is that the system cannot correct and deliver a controlled pressure. The documented data shows a command pressure of 23,000 psi ie: the target for the oulet pressure. As engine speed increases the outlet pressure starts in control and continues to drop by 9000 psi below target pressure. This clearly means the system is out of control and there is no constant pressure. When adding the orginally called for low pressure pump to the circut we show target pressure and control pressure to stay within 500 psi until we begin seeing the low pressure pump start to drop off. As the low pressure pump drops off so does the high pressure pump output.


This is what I do for a living as well and I'm not trying to pick a fight but trying to inform people as to what is truely happening on these vehicles. The data I have presented is real world testing and I've been chaseing the why's for quite some time. As we begin to push the system more and more, the more we learn.http://www.dieselplace.com/forum/smileys/Big Smile.gif

Diesel Tech,


The reason I keep asking for a description of the sytem is because I think the Bosch/GM fuel pump is a little more complicated then most take it for. Even the FASS/Preporator people do not know how it works. It is a 2 stage pump with a low and high side. If I am not mistaken it is alot like a Mazda Rotary engine?? I am thinking about going to Chevy and buying a pump and regulator so I can di-sect and verify.

Bronco,


The reason some of us are running a lift pump is to keep vapors/air in solution by applying slight positive pressure to the fuel as it leaves the tank. With the flash point of diesel being 120 degrees and our fuel temps nearing this in the warmer months due to cooling the EDU and injectors many of us use the lift pump to maintain pressure above zero to prevent pressures below atmosphere from lowering the flash point which is causing free vapors to form. After the factory fuel filter the fuel then goes to the LP pump which is intergrated with the HPCR pump then to the fuel rails where it is injected to the cylinders as directed by the ECM and EDU. I also asked myself the question if the LP pump was structured to deal with air and send it down the return line but I have not been able to positively verify this. Hope this answers your questions. Believe me I am no expert on this system.

Thanks!

Diesel Tech (Steve) - I am under the impression that the stock fuel system works when the engine is left in the stock state (no Juice and/or ECM programming changes). In otherwords commanded fuel pressure = rail fuel pressure over the performance envelope. Is this correct?


By the way, GM saved more than a few bucks by leaving off the lift pump --- example: (400,000 DMAX trucks * $100/liftpump = $40Million)


(assumption - one lift pump plus supporting hardware/circuitry plus installation = $100 ------ substitute your own number)





Alan

Bronco,


The reason some of us are running a lift pump is to keep vapors/air in solution by applying slight positive pressure to the fuel as it leaves the tank. With the flash point of diesel being 120 degrees and our fuel temps nearing this in the warmer months due to cooling the EDU and injectors*many of us use the lift pump to maintain pressure above zero to prevent*pressures below atmosphere from *lowering the flash point which is causing free vapors to form.*

I think you mean vapor pressure rather than flash point. Flash point is the lowest temperature at which a material can be ignited with a flame.

My point had nothing to do with vapor point to tell you the truth. You can put cold diesel fuel across the right fuel filter media and if it is 7PSI on the dirty side and 6 psi on the clean side it will separate. I was trying to illustrate that the real culprits are pressure differences and air flotation rates.


However, I do agree that hot diesel fuel is in a more ready state to let off some air as compared to cold fuel. The problem with cold fuel is it has the capacity to hold more air. Works both ways.


The right lift pump in relation to overall system pressure will hold the air in the fuel to some extent. However in the case of the JK air issues, I personally believe you are still separating air. Here is why.


The lift pump is pulling dense fuel from the tank and pushing it through the system. Any trapped air in the system will be pushed forward from the higher pressure fuel coming from the liftpump. Where the air pocket goes?, I do not know.


Modifying an engine that has evolved over a century is no easy task. Without proper diagnostic equiptment and control factors, you are never really sure what is going on inside the motor and fuel system. Without scientific proof you are just taking a wag!

OC (Alan)





That's the problem. We have seen and documented this problem on stock trucks as well! Granted it's not very often and there is a problem some where but, it just to close to the edge for me. Now when we modify it becomes much worse as we are operating outside of what GM intended the system to do. What I do know is the High pressure pump is the same one that is on the Cummins engine, less a few mounting changes. I am trying to get a defective pump through a friend of mine so I can take it apart and see for myself what they truely have done. I BELIEVE its a rotorary pistion pump interanally but noone has been able to give me an answer for sure. If that's the case there is two stages of pressure built internal to the pump. The first stage builds pressure to a point the electronics can control and that intern controls the second stage. I've read all the documentation I been able to find but no complete answers at this point in time.


What I can tell you is fuel is sucked from the tank all the way into the inlet of this High pressure pump. Everything in between must be free of obstructions and leaks!


The higher vacumn that you draw on the fuel the more air will be released, so it's easy to see where the problem is. By adding more filtering/restriction to the system, vacumn increases and then more air is released from the fuel. What is needed is a good way to take the released air away from the fuel and there is nothing in the GM system that does that unless it's the High pressure pump assemble. I've had everything else apart, several times.


As for GM saveing a few bucks................... figured everyone could understand that one was mostlikely GM's driveing reason to eliminate the lift pump. Cut cost make more money!

I do not belive GM left out any lift pump to save money. If you removed the factory fuel pump and used a fuel tank mounted lift pump, The HPCR system would never work. The 2 stage Bosch pump is the very essence of the entire system. It allows our injectors to be of a vey unique type. Most injectors create there own pressure within the injector. Not ours. The high pressure is already supplied in the common rail. Obviously you could never pressurize your entire fuel system to 23kpsi so instead the factory pump only pressurizes the high side of the pump and the common rail. If the entire system is left completly stock it is a marvel of modern technology.


I do understand the end user is still left with the dilema of removing what some claim to be excessive fuel particle count below the 10 Micron size. This however is a fact that has still not been scientifically proven to be the root of all injector failure.


Further more the performance enthusiast that require more fuel flow are requiring something the truck was never intended to do. Not a bad thing, just not a problem GM created. The Duramax was the best when I bought it and after 3 months of particiapating on this forum, it is finally the best in my opinion once again.

Diesel Tech,


I have spent many hours podering a method to release air in the underhood area. As long as the system is a vacum type system you are will never be able to open the system. If a lift pump was installed at the tank and a bleeder on the JK system, you would have something. You then run the risk of violating this 16 page PREPORATOR patent I have here in my office. It would not be a direct infringment but it could possibly fall under the doctrine of equivalents patent infringement. Never the less if you were not planning on going to market it could be done. I have thought about a bubbler type of unit . Like on the top of brewery tanks. Or you could run a line all of the way back to the tank.

a bear


"The fuel is drawn from the tank by the low-pressure pump through the Electronic Driver Unit (EDU). "


You must be taking this information from a Bosch description, as GM doesnot have a low-pressure pump in the system! http://www.dieselplace.com/forum/smileys/Ermm.gif So what we are doing is adding the low pressure pump that Bosch had called for in the first place! GM must have figure it works OK without it so let's save a few bucks! Cummins uses the same system but runs the low pressure pump. If you follow the Bosch manual it specs. the low pressure supply to be 13 - 15 psi, not 0 - 15 psi.


"The injector, with a constant injection pressure fed to it, can now open, stay open and close as directed by the ECM and EDU, depending on various sensor inputs, to achieve effective combustion for the conditions present. "





This is the key to the whole system, constant pressure! The 9000 psi loss I have described to you is not acceptable. The system commands a fixed pressure to be at the injector and the regulator adjust to that pressure. What I am describing (possible not good enough to you) is that the system cannot correct and deliver a controlled pressure. The documented data shows a command pressure of 23,000 psi ie: the target for the oulet pressure. As engine speed increases the outlet pressure starts in control and continues to drop by 9000 psi below target pressure. This clearly means the system is out of control and there is no constant pressure. When adding the orginally called for low pressure pump to the circut we show target pressure and control pressure to stay within 500 psi until we begin seeing the low pressure pump start to drop off. As the low pressure pump drops off so does the high pressure pump output.


This is what I do for a living as well and I'm not trying to pick a fight but trying to inform people as to what is truely happening on these vehicles. The data I have presented is real world testing and I've been chaseing the why's for quite some time. As we begin to push the system more and more, the more we learn.http://www.dieselplace.com/forum/smileys/Big Smile.gif





Diesel Tech,


This may help you find the missing LP pump and bring things up to speed for you. http://www.dieselplace.com/forum/smileys/Big Smile.gif Also a few other good things that can be appreciated about the DMax


http://www.duramaxdiesel.com


Habanero, ThanksEdited by: a bear

WOW! Don't get Charles Ekstam involved in this one. He will tell you the pressure drop you see and ireneous control issues are actually air moving through the system.

My mercedes is converted to burn vegetable oil, and as part of the conversion, I have a lift pump that pushes the oil through its own filter. This takes the load off the factory lift pump. I have a Racor filter as the oil filter, which has several inlets and outlets. I use one of the outlets as a return to the tank (through a check valve). I realize you need a higher volume lift pump for the duramax, but why wouldn't this system work on the truck? My veggie line is always pressurized at 1-2 psi (the cracking pressure of the check valve) until the filter clogs. Why do you need all the fancy regulators and valves and such? The check valve should regulate it okay, just find one with the cracking pressure you need.

Any exact makes you have in mind?

My point had nothing to do with vapor point to tell you the truth. You can put cold diesel fuel across the right fuel filter media and if it is 7PSI on the dirty side and 6 psi on the clean side it will separate. I was trying to illustrate that the real culprits are pressure differences and air flotation rates.


However, I do agree that hot diesel fuel is in a more ready state to let off some air as compared to cold fuel. The problem with cold fuel is it has the capacity to hold more air. Works both ways.


The right lift pump in relation to overall system pressure will hold the air in the fuel to some extent. However in the case of the JK air issues, I personally believe you are still separating air. Here is why.


The lift pump is pulling dense fuel from the tank and pushing it through the system. Any trapped air in the system will be pushed forward from the higher pressure fuel coming from the liftpump. Where the air pocket goes?, I do not know.


Modifying an engine that has evolved over a century is no easy task. Without proper diagnostic equiptment and control factors, you are never really sure what is going on inside the motor and fuel system. Without scientific proof you are just taking a wag!





I installed a Mega filter post oem and had "air" issues until I installed a lift pump.I used a piece of 3/8" clear tube fastened to the bleeder port of the Mega filter head to monitor the buildup of vapor/air.It works very well and I continue to watch it after a filter change and whenever I have the hood open.Any "free air" whether it is pushed through with a lift pump or sucked from the engine driven pump would show up in my clear tube.Am I wrong on this?


Blake

afp1,


You were not forgotten about. I looked for a reg. for diesel use in the lower pressure range to no avail. I will chime in if I come across one. A adjustable pressure cracking check should also work for what you have in mind. I had purchased one for the same purpose a few months back and decided not to get full of diesel and install it. I was happy w/ the needle valve. Or just lazy.http://www.dieselplace.com/forum/smileys/Big Smile.gif

Steve - Thanks for the explanation. I knew from the Mega Filter air trap problems that others had encountered that we had small amounts of air in the system. Each truck seemed to be different. A_bear, Kennedy and Chuntag(?) spent a lot of their personal time trying to track down all those sources of air in the fuel system to make their Mega fuel filters less prone to this phenomeon. They all eventually ended up with lift pumps for this reason. Also, it does not surprise me at all that there is a wide variation with the fuel rail pressures on the various trucks at this point.


Bronco - Whether GM left the lift pump out or not, we will probably never know. However, the auto manufacturing business it a tough field to compete in. GM certainly has an engineering staff that is always looking to cut costs anyway they can. The reason I attempted to show the cost savings above is because the numbers can add up quickly. Very tempting. By the way,,,,, what happenned to the "under the hood light" in your 2003 truck? The 2001 and 2002 models have one! There are other examples.


Regards,


AlanEdited by: OC_DMAX

Hello OC DMAX,


I was trying to word it in such a way that I only gave credit to bosch and Isuzu. Allison for that matter. The GM part still leaves much to be desired. When I first bought my truck I took a friend out to show the engine off. I was bummed there was no light. After griping for a while I got over it. The light is over rated anyways. Do you ever need to see under your hood in the dark? If you do, will you have the tools/parts and skills required to fix??


I am really just trying to say that after visiting a sight like this, where there are so many people buying/selling and being loyal to the aftermarket community, you can really loose sight of the fact that the GM light duty pick up is one bad mother!Edited by: Bronco

A bear,


Thanks. I'd think diesel would be easier on stuff than alcohol, but I am not sure...................

Blake wrote: installed a Mega filter post oem and had "air" issues until I installed a lift pump.I used a piece of 3/8" clear tube fastened to the bleeder port of the Mega filter head to monitor the buildup of vapor/air.It works very well and I continue to watch it after a filter change and whenever I have the hood open.Any "free air" whether it is pushed through with a lift pump or sucked from the engine driven pump would show up in my clear tube.Am I wrong on this?


Blake


Hello Blake,


Without knowing exactly where your clear tube is and how it is positioned I can not tell you what is happening. It does appear the lift pump is minimizing the pressure difference across the mega and inturn minimizing the air separation. Another slight possibility is that you are now just pushing the air through so quick that it does not have time to float to the top. That is when air flotation rates come into play. Air only floats so quick. If the fuel flow is great enough, air will never make it to the top. It is complicated to say the least. It has taken others 14 years to develop a product that even comes close to explaining and solving this phenominom. I am learning more everyday and that is why I constantly bring up these issues. Every time somebody else writes, I read and learn from there experiences.

Bronco,


I have the Mega mounted under the airbox and the clear tube runs from the bleeder up to the top of the radiator fan shroud area.I have installed a petcock on the end to bleed air after filter changes etc.


After lift pump intallation I still see a significant amount of air accumulate in the tube anytime I change the oem filter so it still seems to trap the large slugs of air introduced into the fuel system.


I'll post a picture if you want if my explanation is confusing.


Blake

FWIW, before adding a lift pump I removed the strainer from a clear glass in-line fuel filter and installed it on the bleeder port of my mega filter. The bleeder screw was on the opposite side of the clear filter. This set up acted as a sight glass so I could see the fuel level in the filter. After bleeding the filter, a short ride around the block would empty the sight glass of fuel. The Mega head has a long inlet nipple that extends into the filter, and this is what traps the heat/vacuum induced vapor circulating in the OEM Dmax fuel system. Initially I also had a small inline fuel pump and check valve connected to the bleeder port. Every few days I would run the pump to bleed the filter into a bottle (Chuntag95 had the same setup). This worked and I had even entertained the idea of plumbing the pump output into the return line. However, I ended up with the lift pump, which seems to be a better solution. Now whenever I check the Mega bleeder by running the lift pump with a pushbutton mounted near the headlight, I get a burst of fuel when the bleeder is cracked open. The first flow of fuel does contain a few bubbles but it immediately turns to a stream indicating that the filter was full of fuel.
http://www.dieselplace.com/forum/smileys/Geek.gif

I have same set-up as NWDmax. Roughly 3 foot of clear tube from Mega bleeder port, with petcock on end, coiled between airbox and radiator. Prior to liftpump, could fill up with air in under a week. With lift pump, no air whatsoever. I have to uncoil to get the full effect, but gravity does all the work.


Since I would have an air accumulation related stall every 160 miles or so after installing Mega, I spent a lot of time trying to find source of air entry with no success. After lift pump, closing off pressure adjustment loop around pump (full lift pump pressure applied to system), I wan not pushing out fuel anywhere. I have concluded that air was just simply "outgassing".


Added benefit of clear line above Mega, I can use the level of fuel pushed up the line to set my bypass, which regulates pressure I am introducing in system. At least until JK finally finishes his guage!!!! John, whats the latest?


Hope this makes sense.

Just FYI, the little pump we/they are using will just cross over to about -1"hg at 250HP (stock) on a stationary dyno. Under dynamic road conditions, it gets worse.





At 450+ it will cross to -10"hg or more. There is still no appreciable air in my bleeder as I believe there is not sufficient time for the vaporization to occur.





No special air removal gizmos, no super lift pumps (although I AM investigating the potential) just 495+ to the ground...





Still haven't seen anyone show a documented gain by adding a lift pump. Not saying it isn't there to be had, just not proven...

Thats really to bad JK had to chime in when he did. We were really learning something here. I wonder how long the list of people with mega and air related problems would have gotten with out JK's .02. Have any of you ever asked for a refund or a free lift pump to correct your problems that JK's product has caused you? Edited by: Bronco

Well I was doing some looking around and this article certainly seems to support what Diesel Tech has been saying about a regulated supply pressure being needed for HPCR performance.


http://www.dieselpage.com/art0500rf.htm


Nice looking unit, I don't think I'd want to maintain 60 psi on my ECMs, though! Now if there was one for 6 psi!http://www.dieselplace.com/forum/smileys/Big Smile.gif

Hello Idle Chatter,


That was some excelent reading. Ford suffers the worst out of the big 3 due to the fact that they make much of there injector pressure in the injector itself. That is why they need the 60 PSI inlet pressure and then the injector takes care of the rest. They have had many more times the performance and injector related issuses than the Dmax ever has. I would not be suprised if that little device FORD crafted up was not some type of air separater as well. You would have to measure the return line for air and then compare it to the intake side.


The only reason I mention the air part is because I have heard personal testimony as to the effectivness of the air separators on Ford. Ford really benifits. It does not mean the GM will benifit.


The reason I keep asking about the GM system having air removal capabilaties is as follows. The stock system works by sending a constant flow back to the tank via a regulator and return line. If the engine demand were to ever exceed the fuel pump supply then the regulator would close and ALL fuel would go to the engine. This would include any air as well. Normally there would always be some going back to the tank however under high HP conditions you are sending it all to the engine. The FASS and PREP are no different. If you exceed there delievery capabillatys they no longer are effective.

Bronco, a little off topic and no offense.


We all, too well, know your feelings towards JK, but do we have to hear them all the time. Everyone is entiltled to their opinions and responses and I value both yours and JK's. I can decide on my own what to do with the information.


On-topic, I do run a lift pump and the mega filter, I did have a little air issues, but the pump took care of it. The biggest benefit for me was the bleeding after a filter change. Turn on the pump, open the bleeder, what a snap. I do run a by-pass regulator and run 1psi at the mega dirty side bleeder port at idle.


I didn't notice any difference with the performance or fuel mileage, though. I do feel good because I run 3 filters now (the lift pump has it's own filter).

Thats really to bad JK had to chime in when he did. We were really learning something here. I wonder how long the list of people with mega and air related problems would have gotten with out JK's .02. Have any of you ever asked for a refund or a free lift pump to correct your problems that JK's product has caused you?


Several people, including myself, proved there was air/vapor within the system in stock configuration. No lift, no mega, no nothing. JK's product did not cause a problem, it highlighted it for a very few people. I believe he refunded money to whoever wanted it once the tendency was found. He also made all new buyers aware before purchase after it was figured out.


Just like the work you are doing with the air filters, others did with fuel filters and lift pumps. It all needs to be done sometime and there is almost always a vendor involved.

Thanks John,


I was curious as to what the pressure draw down would be w/o inertia forces involved. With 10" HG while stationary I would say that fuel line size and corresponding line friction also plays a role in the pressure drops we see. As I think about the monster lift pumps a few folks are interested in, shoving a watermellon through a pee hole comes to mind. http://www.dieselplace.com/forum/smileys/Ermm.gif 495 @ the rear wheels ----- Not bad for what some of our so called TECHnical experts consider a fuel starved engine.


On edit: Like Chris said the MEGA filter did open up some eyes as to what was taking place in our fuel system. Lots of good/usefull information has evolved since this finding. Not to mention that it is a excellant fuel filter with data to back it up.Edited by: a bear

I've got a pair of different pumps to test and see what happens. They'll deliver plenty of volume (used as singles) IF the lines will allow.





No need to regulate either...

The supply lines on the Duramax are quite large compared to what the others use. So were not trying to shove too much through them! According to pump manufactures the D-Max line size is more than enough to support fuel delivery upto 900 Flywheel Hp. So lets forget about line size as the problem. Now the reason GM made it so big was because they knew about pressure losses under vacumn conditions which they were running the system under. I am getting the Bosch design manual scaned that shows the lift pump. lo pressure pump and high pressure pump all in there design rules, maybe then everyone will understand what's going on here.

DieselTech,


How do you plan on maintaining lift pump pressure X while maintaining the desired constant pressure Y at the LP pump suction throughout all loads/RPM's without a line friction coefficient of zero. No pump of any pressure/volume with or without a regulator will accomplish this which again brings us back to line size/length including all bends and fittings. There will always be a line pressure drop as UVL is reachedEdited by: a bear

To all of the pioneers in the air research arena. You have done great work and made a really neat sytem using an ACDELCO lift pump and bypass setup. If I was on a total budget and needed something quick,easy, clean and a great aid for a stock truck your setup would certanily be the ticket. Thank you!


In regards to air separation, to this point nobodys homemade system actually removes the air. You are only moving the air around or keeping more of the air entrained . You are not removing it out of the system. It still goes one of two places. Directly to your combustion chamber or directly to your fuel tank via the return line. Unless a bleed off method is provided, it will never be removed.


As far JK and myself is concerned. Well it is nothing personal. Any vendor who prints fiction as fact is only doing a diservice to diesel owners. I really have only mentioned him or confronted him 2-3 times here on the PLACE in 3 months. So if you think it is excessive then you are getting your information elsewhere. Now that I have made my feelings abundantly clear I will try to refrain from comment. Well hell, while we are on the topic, you know that exaust manifold bump that is removed? Did anyone ever ask an Isuzu engineer if it was placed there on purpose? You know to provide equal cylinder pressure so that the engine could perform as effeciently as possible? No way to know with out asking. I am finished now.


Finallly the monster lift pump setup, regardless of manufacture works simply like this. You install a pump as close to the fuel tank as possible. Preferably lower. You include a regulator that is immediatly after the fuel outlet of the pump but not blocking flow. You set the regulator to a predetermined pressure. Due to the enormous size of the pump you will be returning a very signifigant amount of fuel to the tank. The return line is only 3 feet long. It travels from the outlet of the pump directly to the tank. You are running a moster pump that is constantly providing to much fuel. The extra fuel goes directly to the return line. However at any given instance the regulator on the return line can close down and this immediatly will then send mega amounts of fuel to your engine via the main unubstructed fuel line.This is exactly how any high horepower drag car fuel system works. The only variance would be the addition of a technical and expensive voltage control box that limited the votage to the lift pump motor. Full voltage would only be applied when the fuel demand is great enough. This way you never draw more current from your battery then required and you do not burn up your lift pump motor.


I apoligize to anyone who does not like me bringing new ideas to the table. I have never been much for conforming.

Bronco


Your technical and expensive voltage control box is sitting just across the table from me.http://www.dieselplace.com/forum/smileys/Big Smile.gif As far as the oversize pump goes what I'm working on finding is one that will supply the needs at WOT so I then can cut the output down with our voltage divider circut. Useing this method reduces motor/pump wear as the pump runs at slower speeds until it's needed. The problem has been finding what is needed that will work with diesel fuel and have a min. of 3000 hours of service life.





a bear


If we provide enough volume to the Factory Bosch pump, Low pressure will be controlled by the return regulator we have installed with the lift pump. Line losses for bends and such along with the increase and decreaseing demands from the Bosch pump will also be handled by the same regulator. The Factory computer control of the Bosch 2 stage pump will handle the needs of the injectors and regulate high pressure just fine. We already have the system working but it's with a electric pump that is design for low duty cycle usage, ie: race cars. So the problem is finding a pump that will deliver 220-250 GPH, be compatable with diesel fuel and have a service life of something more than 3000 hrs. If your looking for something for a stock motor the current Fuel Preporator or FASS systems will do it for you. We are just looking to see if we can find one that will meet the needs of all our applications in one pump. It may turnout that this is not practical but at this time I'm not willing to call it quits just yet.

As far JK and myself is concerned. Well it is nothing personal. Any vendor who prints fiction as fact is only doing a diservice to diesel owners. I really have only mentioned him or confronted him 2-3 times here on the PLACE in 3 months. So if you think it is excessive then you are getting your information elsewhere. Now that I have made my feelings abundantly clear I will try to refrain from comment. Well hell, while we are on the topic, you know that exaust manifold bump that is removed? Did anyone ever ask an Isuzu engineer if it was placed there on purpose? You know to provide equal cylinder pressure so that the engine could perform as effeciently as possible? No way to know with out asking. I am finished now.


Finallly the monster lift pump setup, regardless of manufacture works simply like this. You install a pump as close to the fuel tank as possible. Preferably lower. You include a regulator that is immediatly after the fuel outlet of the pump but not blocking flow. You set the regulator to a predetermined pressure. Due to the enormous size of the pump you will be returning a very signifigant amount of fuel to the tank. The return line is only 3 feet long. It travels from the outlet of the pump directly to the tank. You are running a moster pump that is constantly providing to much fuel. The extra fuel goes directly to the return line. However at any given instance the regulator on the return line can close down and this immediatly will then send mega amounts of fuel to your engine via the main unubstructed fuel line.This is exactly how any high horepower drag car fuel system works. The only variance would be the addition of a technical and expensive voltage control box that limited the votage to the lift pump motor. Full voltage would only be applied when the fuel demand is great enough. This way you never draw more current from your battery then required and you do not burn up your lift pump motor.


I apoligize to anyone who does not like me bringing new ideas to the table. I have never been much for conforming.








Bronco,





Best be ready to back up the fiction claim.





As for your lift pump install/layout scenario, it is obvious to me you haven't a clue...

Bronco,


"Now that I have made my feelings abundantly clear I will try to refrain from comment."


I am glad you are refraining from further comment about JK, because I am not interested in yours, mine, or anyone else's feelings about other people. I am only interested in facts and careful opinion concerning the topic at hand. If JK is giving us fiction, then prove it by superior facts, logic, and reasoning; without any negative emotion.


BlaineEdited by: afp1

Has anybody actually run with and without a lift pump to verify gains? I know from past work with high pressure pumps (55,000 psi) that a regulated inlet pressure is the optimum setup. However, it is not always necessary to achieve the same results. I do believe a lift pump does more for the engine than keep the air from forming in the filters. It provides a constant source of fuel at all engine demands which increases the response time of the H.P. pump regulator. I think before people go spouting off that certain peoples lift pump setups, air removers, magnetic re-aligners, etc, are the best or don’t work as advertised should get some hard facts on a dyno. I don’t mean reading that so and so said they ran this with that on a dyno, but a carefully conducted study of the facts. Run them all on the same truck, with the same fuel, on the same day, on the same dyno. Then and only then will this be resolved. In the meantime enjoy what you have and look forward to summer and no mixed fuel.http://www.dieselplace.com/forum/smileys/Big Smile.gif

Dave


We have done just what you are asking and the answer is yes it helps. Some truck more and some less. Same truck, same day, same dyno. I believe that as the systems get older it seems to help more than it does on a new or low milage unit when in stock form. When the Hp is increased via performance modifications it really begins to show. We have found as much as 30 RwHp gains just from adding a controlled lift pump to the system! The issue I have is to find a pump with the life span that I feel we need that works. So far I have not found that. The Fuel Preporator or FASS will work for most stock trucks but as the Hp goes up you can over run what they can handle. As I've said before 220 - 250 GPH is what were looking for.

http://www.dieselplace.com/forum/uploads/Bosch_HP1.png


Here is the recommended setup from Bosch. Item # 3 is the Lift pump that GM left off our trucks! Item #6 is the Bosch High pressure pump.

Diesel Tech,


Not arguing just looking for clarification. First how do you arrive at the needing 225-250 GPH at WOT? Curious how it gets so much higher than the normal of 7GPH at cruising and 50 GPH at WOT on a stock motor.


Secondly I see the diagram you sent. It does indeed show a pre supply pump very near the tank. However it does not state whether the high pressure pump is the exact same pump that is on our Dmax. Is the pump in the digram the exact same pump as the Dmax? I only ask because the Cummins will not operate it the VR44 lift pump burns up or is removed however the dmax operates all day long with no pre supply lift pump?

How many 6.2 diesels did you see with the lift pumps on the frame rail. when they froze up because of water in the fuel the truck wouldn't start. i don't think gm wants to go down that road again. replaced many of them in the 80's and early 90's. 1 less part to fail = more money saved at first and in the long haul. I have a hard time believen that gm left out the lift pump if bosch told them it was required for the system to function.after all they are in this one together with technology that will take us and the diesel well into the future. bosch is the inventor of electronic fuel injection and when all is said and done, they will be the one's to profit from it. we may be the guinnipigs for the future of high performance diesel trucks.

....So the problem is finding a pump that will deliver 220-250 GPH....


Lets see, my fuel tank holds about 25 gallons, that means at 250 GPH, I would use a tank of fuel in 6 min. I'm not driving a Ford here. http://www.dieselplace.com/forum/smileys/Big Smile.gif

....So the problem is finding a pump that will deliver 220-250 GPH....


Lets see, my fuel tank holds about 25 gallons, that means at 250 GPH, I would use a tank of fuel in 6 min. I'm not driving a Ford here. http://www.dieselplace.com/forum/smileys/Big Smile.gif
you could also get a 2000 gal tank installed in the bed to make sure you would have plenty of fuel to get across town and think you could even use one of those high speed filler nozzles to fill your tank.

....So the problem is finding a pump that will deliver 220-250 GPH....


Lets see, my fuel tank holds about 25 gallons, that means at 250 GPH, I would use a tank of fuel in 6 min. I'm not driving a Ford here. http://www.dieselplace.com/forum/smileys/Big Smile.gif



you could also get a 2000 gal tank installed in the bed to make sure you would have plenty of fuel to get across town and think you could even use one of those high speed filler nozzles to fill your tank.


All that weight might cut down on my fuel economy.

...As for your lift pump install/layout scenario, it is obvious to me you haven't a clue...


I'm fairly new to all of this. What is wrong with what he described? It sounds pretty close to me. What am I missing??

JK WROTE:


Bronco,





Best be ready to back up the fiction claim.





As for your lift pump install/layout scenario, it is obvious to me you haven't a clue...


JK, I have seen how these little pissing contest turn out. I will reply and then 4 or 5 of your little cheerleaders will gang up on me. After 2 days of complete BS you and your mob will have done your best to twist around every little thing I have written. In order to save much time I will point out 3 of the most recent examples of you sighting fiction rather than fact. I will go no further. I will not waste anytime digging up past threads that prove your discrepancys and misinformation.


1. You are quoted in this post that from reading my example of a lift pump install/lay out scenario that you (JK) can obviously tell I (Bronco) have no clue. In response I will prove this very statement is false.


a. For some strange reason Diesel tech knows exactly what I was trying to describe.


b. FASS and Preporator unit work exactly as I decribed .


c. Take the time to look at a multi outlet fuel pump. You regulate the return as to not impede the main supply line. JK, because I want you to understand, just imagine a splitter coming off of your outside house faucet. You have two 5/8" 30 foot hoses conected, one to each port. Both hose outputs are measured and have exactly the same flow rate. You close the outlet of the hose that is watering your garden. What happens to the output flow rate of the hose in your flower bed?? Flow obviously goes up. Almost doubling. Hope you now can visualize how return stlye regulation operates.


2. In a past thread you(JK) critized me and said for a guy with 719 post I should know how dirty air equates to silica in the oil. I replied and said I knew but wanted to hear your version. You have still never explained to me in your own words how this takes place. Untill you do I consider that a false statement.


3. In this very thread, several have stated having problems with your fuel system modifications. Solutions range from adding a lift pump to drilling the nipple to adding 25 feet of fuel line to priming daily. I can think of no less than 10 individuals who have had problems. How many have you sold? What is your failure rate?


4. One more for good measure. You once wrote on your website that with out the use of aftermarket filters a person will certainly have injector and fuel related problems. That statement is complety false. There are just as many people on this sight alone, that have had problems with and with out aftermarket filtering.


JK I just am alarmed at how many times a thread will be going one direction and you will chime in and change the entire flow of the thread. You also get really sore when someone post new info before you.( You ranted about copy right infringment when the all 8 replacement TSB was released) . In your website tech tips area when you talk about air flow, it almost word for word from the BANKS literature. Dont talk to me about copy right infringment.


5. You also state on your website that if an electronic power enhancing device is not listed on your sight then it is not worthy of purchase. This is completly untrue. You do sale many good ones, however you left out other solid contenders.


In my opinion, there is nothing humble about your opinion!


What next? Where do we go from here? Do you come back with your rebuttal? Do your lynch men try to hang me? Do you threaten me with legal actions? Do the not always impartial moderators change the flow? &

Bronco


These numbers come from the amount of fuel required to make 700 FwHp + the amount returned to the tank in the factory return system + the amount returned by the new regulator system. Like I said in previous post if your only looking to run stock Hp this much is not needed! From what I have been told the Duramax and the Cummins High Pressure pump are the same less mounting brackets. The reason the Cummins quites when the lift pump fails is the is no bypass for the factory lift pump. So when it quits there is no fuel flow to the High pressure pump. Since you have had a Fuel Preporator and Fass, this problem has been address in there designs.


Dmaxcan


This amount of delivery is only required in High Hp applications, much less is required for highway cruiseing.





Kennedy


There is a problem with the system, why must you always start a pissing match when your not involved with the solution.


Let's try and get this thread back on track and find a solution. For those of you wishing only to run the truck at stock upto +100 Hp performance levels I believe either the Fuel Preporator or Fass system will do the job for you. For the rest of us Hp junkies were working on it.http://www.dieselplace.com/forum/smileys/Big Smile.gif

OK guys, quit fighting! Bronco, you did a great job explaining the differences between the Preporator and the fass.


All of you are in a quest for ultimate diesel performance through the development of a complete and adequate fuel filtration and delivery system. In this post do not think of me as a vendor but as just another person looking, as you, for the answer to these problems. That where I was 14 years ago. I realized that the inconsistant performance of the 'over the road' diesel engine was not because of problems of the engine. Specifically, when an engines runs poorly and then improves, then runs poorly again, it is not in the engine or the engine would 'shell' itself. This did not happen. The variation came from changes in injection timing changes, etc, etc. This is what started me in the direction of what later became product marketed under a registered trade mark. As far as the current product having flow and pressure limitations, we are (now I am a vendor) in the process of extending the product line, as quickly as possible, to meet the challenge of the different applications. (now, not the vendor) You are all on the right track in realizing the need to supply an adequate pressure flow of fuel to the system, whatever type engine it may be, that meets and or exceeds the demand of the engine at all times. Remembering that any of the injection pumps or combination lift pump/injection pumps are a positive displacement mechanism with which the required pressure flow requirements can be calculated. Once known, the supply system can then be designed that meets these requirements. Remember that air entrained in fuel is not my idea, Mother Nature did this. Cavitation in a pump is very well understood, however the creation of a system that fixes all of this was not previously available (oops, the vendor side of me got out again). Catapillar issued Special Bulletin 651-1250 in March, 1990 that details the normal 10% air found in diesel fuel. In this bulletin Cat is selling a site glass so the customer could see the air/vapor and not blame Cat for low power. Cummin's explains in detail in their Service Topic 5-135, 1965, why spin on fuel filters are only partially full of fuel when removed for changing. Cummin's did this so that the customer wouldn't think their filters were defective. That service topic is 13 pages of very good info.


Something else to think about. The rating of a filter/supply system has in the past been by measuring the pressure drop through the filter and/or lines and stating this in 'inches of vacuum'. The lift pump is a positive displacement mechanism in which the pressure/flow requirements needed to fill it at any given rpm can be calculated. The 'vacuum feed' concept or pressure flow developed by Mother Nature is only ambient pressure trying to equalize to the lower pressure at the inlet to the pump. This is a very low mechanical energy and is totally inadequate to do the job. In addition, the conduits from the tank to the lift pump are almost always to small to utilize this low pressure flow efficiently. The point is that the 'vacuum rating' method of rating the efficiency of the fuel supply system is in reality the means to rate the IN-EFFICIENCY of the system. Time to think outside the bun!


Building the ultimate engine will not get the ultimate performance results unless the proper fuel filtration and delivery system is included. This is kind of like having the best, in the league pass, receiver on your team and having quarter back that never learned to throw a pass.


Just thought I would throw my in 2 cents worth, for what its worth!


Hope you are all having a great day!

Bronco,


I have nothing against you personally, and I am not one of JKs "cheerleaders". I have in fact argued with him many times in the past and exepct to argue with him many more times in the future.


I do not know what has transpired between you and JK. I have been posting in Internet forums for many years, and I know how easy it is for people to get crossed up over even the most trivial stuff. I think the most famous pissing match I was invovled in--and I didn't even start it--was over the wisdom of hunting with a 9-10lb rifle vs a lighter weight one in mountainous terrain. This little tiff made friends into enemies, and I quit posting all togther for several months becasue of it. When I look back now, it all seems so silly...............


Now in this thread, you did indeed fire the first shot. Maybe it was a result of earlier pissing matches, but fair or not, on this thread the pissing match looks to be all your doing.


As a reminder, JK posted:


"Just FYI, the little pump we/they are using will just cross over to about -1"hg at 250HP (stock) on a stationary dyno. Under dynamic road conditions, it gets worse.


At 450+ it will cross to -10"hg or more. There is still no appreciable air in my bleeder as I believe there is not sufficient time for the vaporization to occur.


No special air removal gizmos, no super lift pumps (although I AM investigating the potential) just 495+ to the ground...


Still haven't seen anyone show a documented gain by adding a lift pump. Not saying it isn't there to be had, just not proven... "


Here is your post in response to JK:


"Thats really to bad JK had to chime in when he did. We were really learning something here. I wonder how long the list of people with mega and air related problems would have gotten with out JK's .02. Have any of you ever asked for a refund or a free lift pump to correct your problems that JK's product has caused you?"


JK's post is informational and based on his experiences and opinions (and completely fair game for debate), while your post seems a bit emotional and a personal slam of JK. While I am not really concerend if you and JK can get along, I would prefer you deal with the grudge privately and not post it publically so we all have to watch it. If you have ever watched a pissing match from the outside, the you know all it does is make all those involved look stupid, regardless of who started it or who makes the best points.


What would be nice is a logical refutation of JKs points devoid of any negative emotion. If you guys would engage in a pointed but non-emotional debate, much good would come from it.


Speaking of a polit and logical disgareement, you said:


"One more for good measure. You once wrote on your website that with out the use of aftermarket filters a person will certainly have injector and fuel related problems. That statement is complety false. There are just as many people on this sight alone, that have had problems with and with out aftermarket filtering."


Actually, the poll on this site concerning that topic seems to indicate otherwise. While this poll is not scientific, it is the only such info I have come across so far. As such, I am very interested in any data on the topic one way or the other.


First of all, not many folks have injector problems. However, the injector failure rate for those not using a secondary filter was 9%, (20 of 218) and the failure rate for those using a secondary fuel filter was just under 3% (3 of 111).


Here is the link: http://dieselplace.com/forum/forum_posts.asp?TID=4529&amp;KW=poll


Blaine

What fuel system mods has Mtomac put on his truck?


What kind of horsepower is he making on a stock fuel delivery system?


I believe he's one of the highest horsepower trucks here so......


Blake

Bronco


These numbers come from the amount of fuel required to make 700 FwHp + the amount returned to the tank in the factory return system + the amount returned by the new regulator system. Like I said in previous post if your only looking to run stock Hp this much is not needed! From what I have been told the Duramax and the Cummins High Pressure pump are the same less mounting brackets. The reason the Cummins quites when the lift pump fails is the is no bypass for the factory lift pump. So when it quits there is no fuel flow to the High pressure pump. Since you have had a Fuel Preporator and Fass, this problem has been address in there designs.


Dmaxcan


This amount of delivery is only required in High Hp applications, much less is required for highway cruiseing.





Kennedy


There is a problem with the system, why must you always start a pissing match when your not involved with the solution.


Let's try and get this thread back on track and find a solution. For those of you wishing only to run the truck at stock upto +100 Hp performance levels I believe either the Fuel Preporator or Fass system will do the job for you. For the rest of us Hp junkies were working on it.http://www.dieselplace.com/forum/smileys/Big Smile.gif





Diesel Tech,


You stated in this post that our fuel system has design problems and that for the ones that are driving stock trucks the FASS or Preporator would be sufficient. I think most already know where I stand on this subject so I won't even go there. Your quest to make a major change to the Dmax fuel system(super pump) does however bring a couple of questions to mind. In addition to the pressure data you say you have taken, have you acquired the remainder of the necessary information needed when trying to maintain a constant 23K injection pressure which is not by design. For example and just to name a couple. How much constant suction pressure the Bosch LP pump seals are designed to withstand before fuel begins leaking into the base. With a vac designed system wouldn't seal integrity be designed to withstand diffriential pressure from the back side ? Has the proper data been obtained which includes turn down rates and injector erosional velocities. Edited by: a bear

What fuel system mods has Mtomac put on his truck?


What kind of horsepower is he making on a stock fuel delivery system?


I believe he's one of the highest horsepower trucks here so......


Blake








MTomac hasn't added anything to his stock fuel system ...I'm in belief he's well over 500 with N2O but under 600 ponies at the RW ...


But it's a guess ...


Mac http://www.dieselplace.com/forum/smileys/Confused.gifEdited by: Mackin

Diesel Tech,


You said earlier that the Cummins and Dmax lift pumps are the same. You also provided a diagram that shows Bosch recomending a pre supply lift pump. If it is true that GM left out a Bosch recomended componet and the end result is performance/reliabllity issues, then would that not make GM directly liable??


As far as your calcultion of 250 GPh for 700 Hp at the flywheel. Can you show me the formula? Is the formula the same for gasoline/alcohol/diesel or does each fuel based on BTU have its own particular GPH required to obtain 700 FWHP?Edited by: Bronco

Thats really to bad JK had to chime in when he did. We were really learning something here.*I wonder how long the list of people with mega and air related problems would have gotten with out JK's .02. Have any of you ever asked for a refund or a free lift pump to correct your problems that JK's product has caused you?


Several people, including myself, proved there was air/vapor within the system in stock configuration.* No lift, no mega, no nothing.* JK's product did not cause a problem, it highlighted it for a very few people.* I believe he refunded money to whoever wanted it once the tendency was found.* He also made all new buyers aware before purchase after it was figured out.*


Just like the work you are doing with the air filters, others did with fuel filters and lift pumps.* It all needs to be done sometime and there is almost*always a vendor involved.

Do people that run Gregs(Landguy) pre filter setups or the Nicktane need a lift pump?

IF Greg sold you something that was faulty he would stand by it, and supply you with whatever it took to correct the problem his setup caused.I'm guessing Nick would too.

Does the stock filter need a lift pump?

Who should I buy from then? The vendor who will stand behind their product? The vendor who blames all problems on a customer(ex. PC)?

This is all I ask as a consumer:
Whoever the vendor may be(I don't care if it's local or internet) ... Please don't sell me something that causes me a problem and then sell me the fix.

PD

p.s. You better believe this...the customer is always right. If he's told he's not. Send the vendor packing!!!

Excellent post F-Preporator. I wish everyone would go back and absorb everything you said and quiet fighting. Simply put. Some folks added too much to the net suction head of the LP pump. This causes cavitation and possible some aeration of the entrained/dissolved oxygen in the fuel. The lift pump took care of that. The inlet pressure to the LP pump only needs to be high enough to prevent cavitation. This might be 5 inches of vacuum or a couple PSI. I will let the experts decide that. I can post a more exact definition of the above terms if necessary. Later! Frank

What fuel system mods has Mtomac put on his truck?


What kind of horsepower is he making on a stock fuel delivery system?


I believe he's one of the highest horsepower trucks here so......


Blake








I know for a fact that his fuel system is 100% stock, no add on filters, no lift pump, no injectors, no mods to the filter head, in tank pick up, nothing. He runs no additives either. Everytime we plug in the Tech-2, his balance rates are just as good as new.

a bear


I think that your thinking I want 23K all the time, this is not the case! I want whatever the ECM is calling for. The example I gave you was when the ECM was requesting 23K. The system would not hold the requested pressure.


"In addition to the pressure data you say you have taken"


I donot know why you say this as the data has been posted all over this site, all you need to do is go look for it! The thread was post by Nick(Diesel Power) but of course you already knew than since I've said quite a few times already!





If the information I have been given is correct on the pumps being the same internally between the Cummins and Duramax, we could then use the Cummins specification which is 13 - 15 psi which I pointed out to you very early on in this thread, several times! This is why we are still pressure testing what the EDU will hold without damage, so we can determine a safe pressure for the system! I would be quite happy with 3 psi constant at all times, not 3 sometimes and 1 other times.


As for "injector erosional velocities" there is no change from stock as I'm not trying to raise the pressure, only maintain what the stock system was designed to do in the first place!


If I had all the answers I would not be discussing the problem I would have already fixed it.


If you donot believe there is a problem then why have you already added a lift pump and extra filter to your own truck? What research and testing did you do to show it was necessary?


Please post all of your test data both before and after for


lift pump installation


filter installation


then the filter and lift pump combination


You ask for our data and we've supplied it, now let's see your's.


Bronco


What I've said all along is I have been told they are the same except for mounting brackets. If GM's testing showed it work OK without a pump then it upto the public to prove them wrong. That a battle I'm not looking at fighting. below is another page from the Bosch book that may shed some light on this.





http://www.dieselplace.com/forum/uploads/Bosch_HP2.png





If anyone really wants to understand the system you can buy the Techincal Instruction book from Bosch just as I did. It's 50 pages of good reading. The calculation for fuel consumtion are not the same for gas, diesel, alcohol. It is also based on the BSFC of the engine that your applying it to. What we did was install a flow meter in the fuel supply line from the fuel tank and the fuel return line into the tank and measure fuel consumtion at given power levels. This along with checking at what flows the pressure started to drop gave us an idea of what would be needed. You can also go to the standyne web site and look at how they rate there filter units and come up with some close assumtions.

Since the site will only allow small pictures, here is the important part of the text.





Design and function of the components


Low-pressure stage
The low-pressure stage (Fig. 1) provides
enough fuel for the high-pressure
section. The most important components
are:
— Fuel tank (1),
— Pre-supply pump (3) with prefilter (2),
— Low-pressure fuel lines for supply and return (5, 7).
— Fuel filter (4) and
Low-pressure area of the high-pressure pump (6).


Pre-supply pump
It is the pre-supply pump’s job to maintain an adequate supply of fuel to the
high-pressure pump. This applies
— In every operating state,
— At the necessary pressure, and
— Throughout the complete service life.

Steve


As I understand it ~


The fuel runs under the FICM simply cools the step up transformers electronics for the injector solenoids .... Seeing as the Cummins HPCR doesen't have this ECU are the then the injectors must be different ??


I've also found this to be interesting reading ....


The ECM increases pulse width to lower pressure, so if the solenoid receives a 100 percent duty-cycle for some reason, pressure will be at its lowest, and performance will obviously degrade. A 5 percent duty-cycle will produce a fuel pressure of 23,200 psi, and a 95 percent duty-cycle feed will produce a 5,000 psi reading. The pressure should never go below 3,000 psi; if it does, something is wrong. The Tech 2 scan tool provides target and actual fuel pressure readings for diagnostic purposes.


Isn't it true that the system isn't designed to run at 100% solenoid duty cycle ?? Could this be the "running out of fuel" problem and it really not a low pressure "supply" problem but a ......


How will driving up the low end of pressure solve the problem when it looks like the Bosch pump will never keep up with 100% duty cycle ??





Mac


Edited by: Mackin

Mac





I donot think you understand what is being stated in your reading. Let's take it step by step


"The ECM increases pulse width to lower pressure, so if the solenoid receives a 100 percent duty-cycle for some reason, pressure will be at its lowest, and performance will obviously degrade."


The solenoid that is being refered to here is the high pressure control valve, not injector pulse width. Next





"A 5 percent duty-cycle will produce a fuel pressure of 23,200 psi, and a 95 percent duty-cycle feed will produce a 5,000 psi reading."


As the high pressure drops below desired pressure commanded by the ECM the duty cycle will go where........................... to 0%, it's trying it's best to keep the pressure at what the ECM has commanded.





"The pressure should never go below 3,000 psi; if it does, something is wrong. The Tech 2 scan tool provides target and actual fuel pressure readings for diagnostic purposes."


Correct, if the system trys to command 100% it mean it cannot lower high pressure down enough, then there is obiviously a problem.


What we are doing with the lift pump is supply the low pressure side of the High pressure pump with the proper amount of fuel so it can make the necessary pressure to feed into the engine.


"The fuel runs under the FICM simply cools the step up transformers electronics for the injector solenoids .... Seeing as the Cummins HPCR doesen't have this ECU are the then the injectors must be different ?? "





Just because the Cummins doesn't have the EDU with fuel running through it doesn't mean it doesn't have one, it does. GM (Isuzu)has used the fuel to provide cooling for the electronics, it's got nothing to do with the injectors.

I was just asking about the ECU and Cummins verses same Injector ... The rest is FRP regulator and duty cycle ...


I'm assuming one can bump up the Rail pressure to ?? But what I'm wandering is the Bosch system as a whole including high pressure pump ever be able to keep up with demand ...Being designed only to run at 95% capacity no matter how much fuel you push at it ...Even at say 30,000 PSI if even possible is it enough fuel WOT ?? Is the rail capacity there for the injectors to fire at 100% cycle also ??


Everything has it's limitations ...


And these guys are looking for yet bigger injectors ....


Jumping on the fence till we find out ...





Mac

Frank &amp; Mac,


Thank you very much.... Well said


Diesel Tech,


When the Mega install on my truck revealed to me that I had vapors in my system I started searching for leaks and posted my findings daily to who was interested the potential areas that I suspected. After going through the system including the tank sender, replacing all quick connects I had eliminated all posibilities of drawing in air. After realizing the temps of the fuel and taking the vac system into consideration and running the numbers I decided to pressure my system only enough to remove the vac the fuel was subjected to. ZERO psi done the trick. The air was gone. I then rested easy knowing that my system was air free along with the POSSIBLE problems that may be associated with it. (NOT PROVEN) Every bit of the data I acquired on a daily basis was posted for all interested parties to view. I had no reason to share this information with anyone other than to help fellow members that were interested and might be experiencing similar problems. I had nothing to sell so I was not obligated to do this. Many here and on the DP can attest to the fact that these findings were beneficial to many. Before this erra it was not realized that we had free air in the system.(A plus for the Mega design) These tests by myself, Kennedy, Bill Plock,and Chris(Chuntag 95) and through exchanged communications shed light on the fact that our stock system does produce vapors under vac. It is still not clear to me that the stock system tolerates this air well but based on the high miles these trucks are starting to see I would think they do.


I consider any information I share to be for the benefit of others and to myself from some of the feed back I recieve. Your adgenda is a little different because you have a product to sell so you should be the one that needs to provide the facts/dangers.


As far as the data you have compiled it is relative to nothing because you didn't even have a clue that the Dmax system had a LP pump and that the system ran by design @ variable pressures. Numbers mean nothing if you don't even know where they should be at any given time. Thats all it winds up being, just numbers. You even stated the information I posted that came directly from Dmax engine site was false. Didn't know thats where it came from did ya. Better find and sell that SUPERPUMP quick as you are quickly eliminating any doubt anyone may have as to where your knowledge base resides. My suggestion to you would be first to learn what you are working on then try to better it.


Edited by: a bear

A Bear,


I really am trying to follow your research. A few questions keep coming to mind.


1. How do you know there is free air in the stock system if it was not apparent untill the MEGA was installed?


2. How do you know that the MEGA was not actually causing the free air?


3. How do you know that the air is now removed rather than just being more easily passed through do to the lift pump pressure?


I am sure 3 real straight forward answers would clear it all up for me. Maybe even save me some money!

1. The air was confirmed by connecting a clear hose between the EDU and the OEM filter per the helms manual. It takes about 15 minutes to connect a clear hose here. Then bleed/crank the engine take it for a short spin and come back and watch the bubbles.


2.The clear hose is attached before the post Mega which proves the Mega not responsible for the air being produced. Note: The Mega has a extended nipple of about 1 1/2" that protrudes below the base to engage the rubber seal which assures that all fuel goes through the element w/o allowing thread particles to enter the clean side. This allows a 1 1/2" air void to collect over time. It is this head design that allows the Mega to trap the air which is already being produced.


3. The air is not removed with the lift pump. The lift pump adds a small amt. of positive pressure to bring the fuel vaporization curve below the vapor point which keep vapors dissolved in the fuel so they will not separate. The fuel through out the system is in the same state as if it was in a gallon jug. No free air.

Hello A bear,


Have you ever performed the Helm test on a bone stock fully funtioning sytem with a clean factory Racor filter?


How does the amount of air in the sight tube on a bone stock system compare to the amount of air in the sight tube when the mega is installed?Edited by: Bronco

I was just asking about the ECU and Cummins verses same Injector ... The rest is FRP regulator and duty cycle ...


I'm assuming one can bump up the Rail pressure to ?? But what I'm wandering is the Bosch system as a whole including high pressure pump ever be able to keep up with demand ...Being designed only to run at 95% capacity no matter how much fuel you push at it ...Even at say 30,000 PSI if even possible is it enough fuel WOT ?? Is the rail capacity there for the injectors to fire at 100% cycle also ??


Everything has it's limitations ...


And these guys are looking for yet bigger injectors ....


Jumping on the fence till we find out ...





Mac





Excellant post ! My take on this all along......


Installing a 230+ GPH pump to recirculate 90 % of the output then send fuel into a POSSITIVE DISPLACEMENT LP and HPCR pump that could give a rats A$$ what your throwing at it because AGAIN they are positive displacement with volume based on engine RPM then have to deal with the possibility of oil dilution. Doesn't seem like a very good move to me. The system is only as strong as the weekest link in the chain.

Bronco,


It is the same. With the Mega filter in the post position the vac was only increased following the Mega. Try this test and you will be surprised at what you see. However it shouldn't be as bad in the Winter.

Now this topic is finally going some where. May I add just a little on the air that some see. Diesel fuel oil does not have a good vapor pressure like most hydraulic oils. Too low an inlet line pressure (high vacuum) permits air dissolved in the oil to be released. The air will collapse back into the oil under pressure and can cause damage like cavitation. Since we aren't seeing pumps going out I would say it isn't a big deal. Now air that is drawn in through leaking fittings on the low pressure side is another matter and probably doesn't matter in this discussion. Later! Frank

A bear,


I will perform the test as you mentioned. I have some clear EATHER hose on order. It is not suppose to yellow/brown so quickly.


In case you have ever wondered, the Preporator has a long nipple as well. It is about 1.5 " long. It has a long shaft that comes out of the middle of the nipple. In between the shaft and the nipple, there is a little clearance all of the way around the shaft. This clearance area is ported directly to the reurn line and then to the fuel tank. This is where the air goes. The long shaft down the middle allows fuel to be picked up off of the bottom of the fuel filter.


There is also a port on the dirty side of the fuel filter that allows any air that may collect on the dirty side to be sent directly to the return line.


Mack,


I think you mis- interpeted the info. The duty cycle was refering to the duty cycle of the fuel pump rather than the duty cycle of the injector itself. Where did you get that literature anyways?? With the Tech 2?


Diesel Tech,


Where exactly did you buy the Bosch manual? I would like to gets me one. Would you email me a larger version of the single page you posted? I exported and enlarged, however no go. Very blurry.Edited by: Bronco

...Have you ever performed the Helm test on a bone stock fully funtioning system ...


Bronco,


Chris (Chuntag95) did extensive testing on his stock truck with clear lines and a sight glass before installing his mega filter. He found bubbles everywhere (see early DP air/fuel filter threads for more info).


http://www.dieselplace.com/forum/smileys/Geek.gif

...Have you ever performed the Helm test on a bone stock fully funtioning system ...


Bronco,


Chris*(Chuntag95) did extensive testing on his stock truck with clear lines and a sight glass before installing his mega filter. He found bubbles everywhere (see early DP air/fuel filter threads for more info).


http://www.dieselplace.com/forum/smileys/Geek.gif

OK I'm new to this part (haven't done much reading at the Page in a while) I'm not saying Chris or anyone who hooked up the clear hoses are wrong. But could hooking up those clear hoses be part of the air problem,hence showing air in the system actually caused by hooking them up? (kinda like hooking up all the new hoses for the Mega?)

Not looking for flames here, just some answers cause I just don't understand.

I'm not saying the factory system is flawless but if you go breaking lines that were designed by bosch to be a certain way it's quite possible to cause the problems your testing for. which then would prove nothing.

Pepperidge,


The Helms manual contains a detailed procedure for diagnosing fuel system problems that includes replacing sections of the fuel line with clear tubing so air bubbles can be observed. Since Chris knew about the potential for air collecting in his mega filter, he went looking for and found “gas” in the fuel before he installed the filter. IIRC, the main “gas” source was the heated fuel under a vacuum coming out of the FICM. Someone (cant remember who) also found that squeezing the fuel line ahead of the clear tubing would produce bubbles. These and other tests by Chris, Tommy, JK and myself convinced us that the OEM system is nominally circulating vapor (gas). There was even a post from RACOR that confirmed this was “normal”. Whether or not this vapor is a problem in a stock system is still up for debate. In my case the vapor collected in the mega over time caused a no start. Adding a lift pump fixed the problem and gave me some noticeable performance improvements – engine runs smoother, quieter, starts quicker and has a seat-of the pants improvement in throttle response.



http://www.dieselplace.com/forum/smileys/Geek.gif Edited by: jbplock

Here's a link that will help shed some light on why the air builds up and does not just pass:





http://www.baldwinfilter.com/engineer/pdf/94-6r.pdf

abear-


Here is an example of what happens when the stock fuel system can't keep up with demand. this is what steve was talking about on my truck. Also, here is a link to the previous thread:


http://dieselplace.com/forum/forum_posts.asp?TID=3079&amp;KW=fuel+pressure


http://www.wackywack.com/images/dmax/fuel1.jpg


http://www.wackywack.com/images/dmax/fuel2.jpg


http://www.wackywack.com/images/dmax/fuel3.jpg


http://www.wackywack.com/images/dmax/fuel4.jpg


http://www.wackywack.com/images/dmax/fuel5.jpgEdited by: Diesel Power

a bear





I have no adgenda as I donot sell fuel pumps or filters! Seems when someone disagree's with you, you don't like it. I make and sell performance upgrades for the computer system and exhaust. The information I have provided is real. You have not pointed out anything to me about a low pressure pump that was not already know to me. If you will look at some of my post I refer to the High pressure pump as a 2 stage pump with one side of that being low pressure and the other being the high pressure side. I've posted the data from Bosch showing the fuel supply pump designed into the system but you continue to stick you head in the sand an ignore it! Why does the Mega filter show more air than stock? It's an easy thing to answer............when you pull vacumn on a liquid it will try and remove any air trapped. But of coarse you should have already know that before you installed the Mega filter. Since the Mega filter adds additional restriction to the stock system more entrained air is released! So the cause of additional air is from the Mega filter install. This is just basic stuff. So by adding the filter you are forceing the High pressure pump to pull more load and thus put more load on the engine to drive the pump, since it's a postive displacement pump. By adding a supply pump as called for by Bosch in the orginal design you remove load from the High pressure pump and eliminate the vacumn condition so the entrained air is not released from the fuel. All I've said is to make sure to keep the pressure positive in all conditions, just the same as Bosch has called for. The question is to what pressure should it be. I can only guess at the answer that's why were doing the testing on the EDU, so we donot damage it. As I've said over and over again Cummins calls for 13 - 15 psi but I guess there just dummies like me! What happens if you charge (pressurize)the chamber of a positive displacement pump............................ the output pressure gets raised! So as the feed side to the pump changes pressure so does the output side, this is why it's important to keep a steady pressure on the input side!


So now let's talk about variable pressure of the system. First let's start by letting everyone know it's the output side of the High pressure pump were talking about, not the output side of the low pressure within the pump. You must have not been able to read what I've said very well so I will repeat myself again just for you. When the Desired Fuel Rail pressure is call to be 23,055 psi and the Actual Fuel Rail pressure is 14,361.8 psi there is a problem! By adding the supply pump as called for by Bosch the problem went away! We used 6 psi as the set point in the tests. This is fact not fiction!


Believe what you like but the information was provided to help other members. Since you believe you've mastered the system and I donot know what I'm doing this just becomes a pissing match and I'm not going to waste anymore of my time responding to you.


jbplock





"In my case the vapor collected in the mega over time caused a no start. Adding a lift pump fixed the problem and gave me some noticeable performance improvements – engine runs smoother, quieter, starts quicker and has a seat-of the pants improvement in throttle response."


This is the same results we have had by adding the lift pump on both stock and modified trucks! Our feeling is the stock system is passing the air into the injectors cause the output pressure to vary and timing to shift around.


Bronco


I'm a SAE member so I got it through my connections with SAE.

You were right Diesel Tech when you said that if you add a positive pressure to the inlet of LP pump you increase the output of the high pressure. You will increase the output by the same amount of increase on the inlet side. So 3 or 4 PSI doesn't mean anything when working with 23K. Later! Frank Edited by: Frank Blum

Frank





Since you seem to agree that increaseing the inlet pressure will increase the outlet pressure how do you explain the pressure riseing from a vacumn to 23,000 psi? Would it not be a fair statement that there is some gain in pressure as the fuel is feed from stage to stage within the high pressure pump. So an increase of a few pounds on the inlet will be much more than a few pounds on the outlet! If it were a linear function it would be a gain of 23,000 : 1 but we know this is not the case. I would need to know the bore and stroke of each stage and the volume of the area being filled along with the RPM of the pump to figure out what the rise would be, but, the simple test of adding 6 psi to the inlet and having resolved the problem is where I stopped at. The problem is that when the feed (Prepump)system pressure continues to change the pump works harder to try and compensate. By holding it steady we reduce the load on the 2 stage High pressure pump and make the control loop much more stable!

Thanks again Frank!


A 3# suction increase would yield a 3# increase afterwards. A drop in the bucket as compared to 23000 psi. I agree a lift has its benefits for keeping air in solution and convieniance of bleeding, But adding a monster pump to try to replinish 9000 Psi of pressure which is controlled by the ECM and FRP regulator by design is nonsense.

The Bosch fuel pump is a two stage pump. It contains a low side supply pum.(lift pump) and it contains a high pressure pump. The high pressure pump makes it 23K via series of internal plungers. If you do not have the required amount of fuel at the low side pump then the high side pump will never be able to do its job as desingned by Boasch.

I've been reading all this with great interest. I think there's some fundamemtal misunderstanding on the operation of the fuel injection system by many that is causing confusion. My understanding and what I've seen in my reading of the manuals is that there is not a simple relationship between the low pressure and high pressure side of the pump. I keep seeing Diesel Tech make statements related to this fact that are countered with simple positive displacement or more simplistic arguements. The low pressure pump "pulls" the vacuum and fuel and produces a supply volume for the high pressure pump. The supply volume is not simply a reservoir, but is controlled by a complex electro/mechanical process to partially regulate both volume and pressure in the high pressure common rails on the other side of the high pressure pump. The volume/pressure on the intake of the high pressure pump is vital to meeting the design and function of the injection system. All other Bosch HPCR systems other than GMs seem to use a positive pressure supply pump to the low pressure side of the injection pump. In the Ford/Racor article that I posted earlier, there is a blanket statement that: "a good regulated supply pressure to the low pressure pump is vital to the operation of the Bosch HPCR system." Now - I don't know WHY GM thinks it's not necessary for our system, but it appears that Bosch intends it. I strongly suspect that a steadily regulated positive pressure to the intake of the injection pump is nothing but a good thing and probably will greatly ehance the overall performance and durability of the Duramax fuel injection system.


http://www.dieselplace.com/forum/uploads/9E8_dmaxfinj.jpg

I just knew you were going to have trouble with my statement that is why I ran it past my son. He is a senior ME that designs, builds and oversees the operation of high pressure water cutters/knives. They operate at 35K PSI. They also use charge and recirculating pumps to maintain operating pressure.


The only job of the LP pump or circuit, or whatever the hell it is, is to completely fill the cylinders of the HP pump on it's intake stroke. It is a high volume low pressure pump. It pumps GPH period. What ever pressure it builds is determined by the HP pump and a constant flow to it's suction side. The high pressure in the system is determined by the amount of flow through all the various nozzles, return lines pressure regulator etc. If we keep the intake side of both pumps full under all operating conditions there will not be any problems from cavitation or air.


While I am on a roil and have my flame retardant suit on I will give you something else to chew on. 1. Pumps don't suck the fuel in. Atmospheric pressure pushes it in. 2. Pumps do not pump pressure, they pump fluid rated in GPH, GPM, CFPM, etc. 3. There is a lot more to be learned about hydraulics than what we have discussed here on our fuel systems. Right Dave?


One last thought: Hydraulic experts are like gun fighters. There is always some one that is better. I have always made it a point to pick the brain of people I thought could make me better at what I did. The only time I lie is when I don't understand what I know. Please don't read anything between the lines of my post. If even one thing I said helps anyone I will consider my time well spent. Later! Frank http://www.dieselplace.com/forum/smileys/Big Smile.gif

Rail pressure is controlled by throttling fuel at the <B style="mso-bidi-font-weight: normal">inlet[/B] side of the pump, using a pulse-width modulated solenoid valve. That valve only needs to work against fuel pressure generated by the gear-type feed pump, which is limited to about 20psi.

The only job of the LP pump or circuit, or whatever the hell it is, is to completely fill the cylinders of the HP pump on it's intake stroke. It is a high volume low pressure pump. It pumps GPH period. What ever pressure it builds is determined by the HP pump and a constant flow to it's suction side. The high pressure in the system is determined by the amount of flow through all the various nozzles, return lines pressure regulator etc.


Sorry Frank, but that is my last point EXACTLY. The Bosch pump is NOT a simple two-stage pump as you have claimed.


Quote from the GM Tech manual, Engine Controls - 6.6L:


Fuel Junction Block


The fuel junction block is located between the left and right fuel rail assemblies. The fuel junction block consists of the following components:


- Fuel Rail Pressure Sensor


- Fuel Pressure Relief Valve


the fuel rail pressure sensor gives the ECM an indication of fuel pressure. The ECM uses this information to regulate fuel pressure, by commanding the fuel pressure regulator to open or close on the inlet of the fuel injection pump. The fuel pressure relief valve opens only to prevent excessive pressure in the event of a malfunction.


Also:


The fuel injection pump is a mechanical high pressure pump. Fuel is pumped to the fuel rails at a specified pressure. Fuel pressure is regulated by a valve on the inlet of the fuel pump, controlled by the ECM.


On another note - if the injection pump were simply a mechanical process, rail pressure would be low at idle and astronomically high at 3500 rpm since the pump is driven by the crankshaft - no?http://www.dieselplace.com/forum/smileys/Geek.gif

Idle I realize that the pump is not that simple and there is some electronics involve. What we really need is a pump to take apart. My dealer is suppose to let me borrow a used one when if ever they replace one. Same with the injectors. Sounds like a variable volume pressure compensated pump except it is done electronically because a mechanically compensator could not react fast enough. Sounds like the pressure sensor is a feed back device. I would almost bet money that there is fuel going through the PR valve all the time. I will check that some time. As I understand the system, idle pressure is around 5-6k and goes up to 23K at full power. Later! Frank

Yeah, I agree, Frank - we really need more information. I've been digging through the manuals and there are no real clear explanations of the pump. There IS the fuel junction assembly, which contains the Fuel Pressure Regulator. NOW, the fuel pressure regulator "supplies pressure to the pump as commanded by the ECM." That means that it HAS to be between the low pressure and high pressure stages in the process - or it would have NO PRESSURE TO REGULATE!http://www.dieselplace.com/forum/smileys/Approve.gif (Sorry, just getting "invigorated" as I try and piece this together from bits and scraps of information!) So my assumption is that the low pressure section of the pump pulls fuel from the tank and supplies it to a suction plenum for the high pressure section of the pump. This plenum pressure is controlled by the fuel junction, which contains the fuel pressure regulator that "rejects" fuel to the return line in accordance with the signal from the ECM. I think that a "frothy" or fluctuating pressure in the plenum might make it difficult for the fuel pressure regulator to smoothy respond to the ECMs commands and could cause the supply to the high pressure pump to fluctuate high and low of the target values. With the injection process setting pulse width and duration based upon a "desired" rail pressure, a slump in rail pressure will result in a "short shot" on the injection. So, it stands to reason that if the supply pressure is "waffling", rail pressure is also "hunting" and the injection volumes will be low or high on each pulse. Adds more confirmation to my suspicion that a regulated fuel supply to the pump will only help the process occur more closely to design tolerances. This also tends to confirm something that I've felt for some time as far as our system's "air tolerance." Since there is a design fuel return rate from the pump (Minumum is 2.0 oz. in 15 secs. of cranking or "replace fuel injection pump!") The low pressure pump is rejecting a pretty steady volume of fuel from one of the higher points in the fuel system.http://www.dieselplace.com/forum/smileys/Clap.gif

Idle, I don't know if what you just said is correct or not but it sure makes sense. The question I'm left with is, and it's been brought up before, what is the ideal pressure for supplying the LP pump? Someone raised a concern earlier about over pressure being bad for the LP pump. Is there a pressure relief of any type to eliminate this potential problem? Next question directed to the tree outside the window cuz I know there is no answer. Why in hell didn't the general give us a system with proper filtration, proper LP side input pressure/volume and some method for getting rid of the air? Yes, it would have cost us more but it sure would have eliminated a lot of frustration!!!

Idle, the parts of your post that I understand are on the money. Like I said: I sure would like to have a pump on the bench in my shop. I have torn down a lot of pumps over the years and am confident I could figure it out. I have a hunch after reading your post that we are dealing with a servo motor that is throttling an inlet valve to the HP pump. The feedback device is the pressure sensor. Servo systems are complicated and expensive. I have been to a Vickers servo school but that was 20+ years ago and I am sure things have changed a lot. I do still have my books and a #1 son that is up to speed on robots. I have spent several hours on the net trying to find a drawling of the pump that is better than the one the GM techs have from the GM site. Can't find one and am sure GM does not want us messing with the pump. Later! Frank

Good questions, Oldman, and I'm guessing as much as the next guy. The Bosch systems in other applications use lift pumps. Amric stated that the "interstage" pressure is 20 psi. Just making an educated assumption, I'd think that something on the order of 4 to 6 psi might be adequate and "safe." I don't think there's any real danger to the LP pump, as it has to be pretty sturdy to pull so much vacuum. My main concern would be the fittings and channels in the FICM modules on the valve covers. Pressurizing the fuel line forward of the tank (ie: a frame mounted lift pump) will change the fuel system from vacuum to pressure through the firewall quick disconnects, FICM connections and modules, fuel filter head/canister and up to the pump. (Add in pre or post OEM filters). There's been discussion regarding the fact the the factory fuel quick disconnects are really a pressure-sealing versus vacuum sealing joint. The fuel filters are not a problem, so that just leaves the FICMs. I was interested in the findings on the FASS and Preporator, but am not convinced of their total worth (and don't want to wait two months for an "Air Dog") - so I'm looking at a lift pump. Whether it will be an AC Delco unit or a Holley red I have yet to decide. I'm still investigating the Holley as far as suitability and diesel compatibility. A pump of some sort is in my truck's future very soon.

The only job of the LP pump or circuit, or whatever the hell it is, is to completely fill the cylinders of the HP pump on it's intake stroke. It is a high volume low pressure pump. It pumps GPH period. What ever pressure it builds is determined by the HP pump and a constant flow to it's suction side. The high pressure in the system is determined by the amount of flow through all the various nozzles, return lines pressure regulator etc.


Sorry Frank, but that is my last point EXACTLY. The Bosch pump is NOT a simple two-stage pump as you have claimed.


Quote from the GM Tech manual, Engine Controls - 6.6L:


Fuel Junction Block


The fuel junction block is located between the left and right fuel rail assemblies. The fuel junction block consists of the following components:


- Fuel Rail Pressure Sensor


- Fuel Pressure Relief Valve


the fuel rail pressure sensor gives the ECM an indication of fuel pressure. The ECM uses this information to regulate fuel pressure, by commanding the fuel pressure regulator to open or close on the inlet of the fuel injection pump. The fuel pressure relief valve opens only to prevent excessive pressure in the event of a malfunction.


Also:


The fuel injection pump is a mechanical high pressure pump. Fuel is pumped to the fuel rails at a specified pressure. Fuel pressure is regulated by a valve on the inlet of the fuel pump, controlled by the ECM.


On another note - if the injection pump were simply a mechanical process, rail pressure would be low at idle and astronomically high at 3500 rpm since the pump is driven by the crankshaft - no?http://www.dieselplace.com/forum/smileys/Geek.gif





I'll try this one more time. Part of my point resides at the highlighted section of this well explained post. I think we all can agree that the rail pressure is variably controlled by the fuel pressure regulator that resides @ the LP pump outlet. I also think we can agree that it is this valve that controls (variable) rail pressures up to 23000 psi based on the signal it recieves from the ECM. HOWEVER: This does not condem the fact that the LP pump is a pos. disp. pump. Do we not agree that it is ? With this pump being a gear driven pos disp pump based on engine RPM how are you going to force more fluid through it than what it is moving at its current RPM. Is this NOT the way the system is designed to operate ? SO: Running a lift pump at low pressures that may be of benefit by providing convienance and to stop free air would be OK(A Good Thing) This has already been done by several here with great recorded results. Now the kicker: Why do we need a monster pump that will recirculate 90 % of its volume and will probably be expensive as hell to try to push fuel at a LP pump that says to hell with you, I will only move what the engine RPM's tell me to.


Edited by: a bear

&lt;SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Verdana; mso-bidi-font-size: 6.5pt"&gt;Pepperidge,&lt;?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /&gt;&lt;o:p&gt;&lt;/o:p&gt;&lt;/SPAN&gt;


&lt;SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Verdana; mso-bidi-font-size: 6.5pt; mso-fareast-font-family: 'Times New Roman'; mso-bidi-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA"&gt;The Helms manual contains a detailed*procedure for diagnosing fuel system problems that includes replacing sections of the fuel line with clear tubing so air bubbles can be observed. Since Chris*knew about the potential for air collecting in his mega filter, he went looking for and found “gas” in the fuel before he installed the filter. IIRC, the main “gas” source was the heated fuel under a vacuum coming out of the FICM. Someone (cant remember who) also found that squeezing the fuel line ahead of the clear tubing would produce bubbles. These and other tests by Chris, Tommy, JK and myself convinced us that the OEM system is nominally circulating vapor (gas). There was even a post from RACOR that confirmed this was “normal”. Whether or not this vapor is a problem in a stock system is still up for debate. In my case the vapor collected in the mega over time caused a no start. Adding a lift pump fixed the problem and gave me some noticeable performance improvements – engine runs smoother, quieter, starts quicker and has a seat-of the pants improvement in throttle response.
&lt;/SPAN&gt;


&lt;SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Verdana; mso-bidi-font-size: 6.5pt; mso-fareast-font-family: 'Times New Roman'; mso-bidi-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA"&gt;http://www.dieselplace.com/forum/smileys/Geek.gif*&lt;/SPAN&gt;

Good post JbP I kinda see what your talking about but How come the stock system will pass it and some filter systems amplify the problem?
Just curious.

PepperidgeEdited by: pepperidge

I see your point, abear. The HP pump is positive displacement and its output is controlled by input - right? The LP pump is positive displacement and its output will be controlled by input - right? The key is the fact that the LP pump is designed to be pulling an excess of fuel volume to be used and rejected by the fuel pressure regulator. The LP pump is supposed to be doing all this by "sucking" fuel through the whole supply system. It appears that Bosch intends for the LP pump to be "assisted." The fuel pressure regulator is acting like a waste gate to "dump" excess fuel in accordance with the ECM signal. If the LP pump is not pulling sufficient fuel, when the fuel pressure regulator shuts off all rejection and the LP output is insufficient or "surging" then it stands to reason that the same thing will be occurring on the HP pump. I think this is confirmed by many reports of lift pump installations "smoothing out the idle" of the trucks. Seems like the system would suffer most at low rpms with low suction on the LP side and low pressure on the HP side.

I would also guess the LP pump has a built in PR valve. Then again it might not be a positive displacement pump. Later! Frank http://www.dieselplace.com/forum/smileys/Evil Smile.gif

Idle_Chatter,


While researching the air in fuel issue I pulled my tank to check the sender design. I removed the return line and and cranked the truck to catch the return fuel in 5 gal cans. Needless to say the tank was emptied in short order. And this was before I had the lift pump. Yes this pump moves way more fuel than whats needed by the engine and to cool electronics, etc. Part of the reason we use gear pumps and meters in our industry is because the govt. requires precise measurment of fluids and these have the lowest coefficient of fluid slippage. Thats why I feel that you can't cram more fuel through the gears. The volume will be discharged only at the rate of RPM. The smaller lift pumps should be all that is needed to stop free air and promote smoother running.

The idea of the so called monster pump is really very simple. Supply the amount of fuel needed to support the fuel consumption of the engine, return system and new low pressure regulator. I've said it before but I felt it was worth repeating again since the discussion is back on track. The pressure that needs to be applied to the low pressure section of the 2 stage High pressure pump is as of yet undetermined. We know that 6 psi seems to work with no ill affects as several members are already runing it this way. They all have reported smoother running engines and set of the pants change in throttle responce, a good thing. Whether or not we should go up to the Cummins specification of 13 - 15 psi is yet to be determined. I have a EDU under test at 10 psi and will let it run at that pressure for the next month. This is on the work bench not on a truck and it's running 24/7 at this pressure. At the end of the test cycle we will increase fuel pressure to 15 psi and start the test over again. If it doesn't spring a leak at that point I'm going to call it quits. I feel there is no reason to go above the Cummins specification. The size of the lift pump only needs to be big enough to regulate through out the engines operating range, so if your running at stock Hp levels you will need much less than those of us running at High Hp levels. The Preporator and Fass systems will do the job for most of you or you can just get a lift pump rated at 100 GPH. This is what it takes to supply the motor at max stock power output plus the return systems. Holley black is rated for 140 GPH, I'm not sure of the flow rates of the blue and red pumps. The only problem I have with those pumps is they leak and donot seem to last very long. They are also noisey if not mounted on rubber mounts. Try and find something that's rated for diesel fuel and 3000 hours service life. That will get you a pump that will last about 100,000 miles.

The idea of the so called monster pump is really very simple. Supply the amount of fuel needed to support the fuel consumption of the engine, return system and new low pressure regulator.


I completely agree with the need for a pump that can meet these 3 demands, but what filter can flow at that rate? I believe all the the current popular filters CAT, Mega, and Racor all flow 90GPH or less.Edited by: Amric

Now for my two cents. Does anyone know if maybe the HP pump is a variable volume or pressure compensated positive displacement pump? It could be either one or both and would solve many of the pressure/flow/rpm problems. I seen somewhere someone mentioned a servo, which could be used to vary the volume displacement of the pump. As far as regulating the fuel on the inlet side of the pump, my experience with high pressure (36,000 psi) positive displacement pumps is that if the inlet flow is restriced in any way the pump will cavitate and destroy the mechanical componenets of the pumps in a very short time.

The idea of the so called monster pump is really very simple. Supply the amount of fuel needed to support the fuel consumption of the engine, return system and new low pressure regulator.


I completely agree with the need for a pump that can meet these 3 demands, but what filter can flow at that rate? I believe all the the current popular filters CAT, Mega, and Racor all flow 90GPH or less.





That's a good question, I wonder if anyone has tested these to see what they will flow. The test would need to be done with a vacumn on it for those who are running stock and again at different pressures for those running lift pumps.

deletedEdited by: Frank Blum

A couple of observations.


1. Nobody is trying to shove more fuel past the pump than it can use. We are only trying to assure there is an adequate supply for the pump to choose from.


2. When searching for a lift pump I would say choose a pump with a higher GPH rating rather than a high pressure rating. Example. A 5 gallon bucket of water dumped on your head will get you wet in a second even though it was at almost zero pressure. A high pressure nozzle on the end of a garden hose at 50PSi will barely get you wet in one second.


3. IF it is proved that GM is leaving out a vital fuel system componet, then I say Class action resulting in life time fuel system warranty. Not angry rather confused and concerned. I am sure this thread will not stop untill we all have a very thorough understanding of the fuel systems limits and capabillatys. Highlights and short commings.

...my experience with high pressure (36,000 psi) positive displacement pumps is that if the inlet flow is restriced in any way the pump will cavitate and destroy the mechanical componenets of the pumps in a very short time.


And I have read, on this 4M, of several pump replacements. Makes ya go Hmmmmm.

One thing to keep in mind. The Bosch pump does not recirculate high volumes of fuel. As stated earlier, (by I believe Amric) it is "throttled" to control flow.

One thing to keep in mind. The Bosch pump does not recirculate high volumes of fuel. As stated earlier, (by I believe Amric) it is "throttled" to control flow.


I think it does recirculate high volumes of fuel, John. One of the pump diagnostics is to place a hose and container on the pump return fitting. Pull the ignition relay and crank the engine for 15 seconds. If the return volume is less than 2 oz. - "replace injection pump." The supply to the high pressure side from the low pressure pump is "throttled" by the fuel pressure regulator, but the low pressure pump is recirculating an absolute minimum (at cranking speed, mind you) of 3.75 gallons per hour! I'd reckon that it's returning something closer to 8 gallons per hour at engine idle.

I believe there is fuel that goes right through the low side pump. If the high side pump does not need it then it will go right past through the low side. This is dicated by the signal the external regulator receives. If the regulator is commanded to open then the pump will pass fuel right through. If the regulator is closed then all of the fuel flow present at the low side of the fuel pump is being needed by the high side pump.


Yes the intake of the high pressure pump is controlled by throttling the low side. That is what I meant when I compared the system to a rotary engine. The digram shows the low side exit rotating in relation to the high side intake. It is very difficult to control high pressure. It is much easier to control the low side which then helps control the high side. That is why I am confused about cavitation at the high side pump entrance. It almost seems as though it was designed to run with varyable inlet flows?? Sometimes full flow sometimes almost dry?


There is also an amount of fuel going out to the injector itself and returning to the tank. So return flow from 2 different locations.


This is not ment to bbe an authoritaive post. I am moreso hoping someone will read what I wrote and help me understand it.http://www.dieselplace.com/forum/smileys/Approve.gif

The end of the line on the return side is a .0625" orifice...http://www.dieselplace.com/forum/smileys/Wink.gif

Bronco, where are you getting your data? Do you have a drawing of this pump? Later! Frank

The end of the line on the return side is a .0625" orifice...http://www.dieselplace.com/forum/smileys/Wink.gif


Where is the line your talking about located? I have the lines off the return from the Hp pump and find no .0625" orifice in them. I have check all of the return lines back to the quick disconnect on the driverside of the engine and cannot find this orfice you have talked about.Edited by: Diesel Tech

Bronco, clean out your PM box so I can send you a reply. Later! Frank

Bronco, where are you getting your data? Do you have a drawing of this pump? Later! Frank


Hello Frank,


I have cleaned out my PM box. You can send me a reply. What I basically Pm'd to Fred was that I have several sources of information however none of them seem to answer all of the questions that are on the table. The biggest piece of literature I have is an article from Morot Age printed in 2000. It has some diagrams and some literature. If I can figure out how to get it out of my mail box I would be glad to display it for all.


The other main source of data I have is this very thread and other threads that have been posted here on the PLACE. If a guy goes back and re-reads evey post in this thread regardless of who posted it, there is a large amount of info.


I think the real trick here is to try and iterperate what everybody is trying to say. It is very hard to do without a dis-assembled fuel system including the pump sitting write here in front of me. I buy no means have all of the answers yet. Heck I am not even sure I know all of the questions.http://www.dieselplace.com/forum/smileys/Wacko.gif

I think the orifice is only in the injector return line. There's definitely no orifice that I'm aware of in the pump return, and I know from personal observation that my aux tank fuel return connection pumps a steady pressurized 7/16" stream of diesel back into the tank at idle.http://www.dieselplace.com/forum/smileys/Cool.gif

The Helms manual contains a detailed procedure for diagnosing fuel system problems that includes replacing sections of the fuel line with clear tubing so air bubbles can be observed. Since Chris knew about the potential for air collecting in his mega filter, he went looking for and found “gas” in the fuel before he installed the filter. IIRC, the main “gas” source was the heated fuel under a vacuum coming out of the FICM. Someone (cant remember who) also found that squeezing the fuel line ahead of the clear tubing would produce bubbles. These and other tests by Chris, Tommy, JK and myself convinced us that the OEM system is nominally circulating vapor (gas). There was even a post from RACOR that confirmed this was “normal”. Whether or not this vapor is a problem in a stock system is still up for debate. In my case the vapor collected in the mega over time caused a no start. Adding a lift pump fixed the problem and gave me some noticeable performance improvements – engine runs smoother, quieter, starts quicker and has a seat-of the pants improvement in throttle response. http://www.dieselplace.com/forum/smileys/Geek.gif




Good post JbP I kinda see what your talking about but How come the stock system will pass it and some filter systems amplify the problem?
Just curious.

Pepperidge


I believe that the answer is truck to truck variation. I have never had a no start from air/vapor. Some have in stock configuration and others only with added filters. If you can get a large enough volume of air/vapor to pass into the line, you will basically starve the engine of fuel and/or get a no start. I had a clear line on my truck for serveral weeks before adding a filter. I tried all kinds of things and could trap air/vapor at will, but never eliminate it until I added a lift pump. I also was able to put an air trap post Mega that showed I could go for a couple of days with no air and then start passing some (no lift pump yet). It never caused an issue in my truck like it did for others. Was that because the angle of my filter head allowed a slower or more even air/vapor release, so it doesn't kill the engine or cause a no start? Was a line bent slightly different or my high point at a different spot? I have no idea. I do know there are bubbles going through the stock system all the time. I know that diesel will create bubbles when heated up as I tested that very hypothesis. If I could remove the air/vapor and send it back to the tank, I would do that as opposted to just keeping it in solution. I will consider the new unit for Pickups when it comes out and a couple of others prove it to work and show an advantage. (Boy is that going to be hard to sell the wife after all I have spent building my own system, even with data.)